As a fighting game, Virtua Fighter is the best it's ever gonna get for DOA crossovers. If anything, I would call that an honor on Team Ninja's part, given the former's polished reputation.
Why DOA and VF? It's simple. The games have more in common than you think, and I don't think there has been one this potentially well-balanced since Capcom vs. SNK. Sure, one is considered highly competitive and the other highly casual, but in their own right, they're getting there to appeal to a certain field, which is the opposite of their usual crowd. And this, my friends, is a way the both of them can benefit from each other, should the situation ever call for Team Ninja wanting to do an actual full crossover someday. And with the more mature, realistic approach Team Ninja is taking with the DOA franchise in DOA5, the chances of their blending in with each other just got better.
Not to mention DOA is considerably more popular outside Japan, which could help get casual players into the VF universe by fleshing out its story and characters in-game to more than just their unique tools, playstyle, and matchups. Likewise in Japan and with other FGCs (provided the mature approach follows up well), people may see DOA in a more serious perspective than usual...but it all comes down to finding the right balance of gameplay mechanics and casual appeal, while not sacrificing too much on either side.
There's a lot the two games have in common, maybe more than I could count. What also makes this the best crossover idea is that it has the potentially least amount of roster sacrifice compared to any other 3D fighting game crossovers. While most crossover games have a large cast, but only so many have parallels with another, VF and DOA doesn't have this problem because their roster is relatively small and leaves very little room for sacrificing characters in the roster. Anyway, I'll share the list of common factors in the game.
1) Both of the games have a general three button scheme: Punch, Kick, and Guard (in DOA, you can also hold the opposing direction to block)
2) At least one game in the series was developed on a common arcade board -- the Sega Model 2. In the same token, Dead or Alive 2 was also developed on a Sega arcade board-- the Naomi. However, Virtua Fighter 4 was developed on an upgrade of that particular board called the Naomi 2.
3) In both games, their earlier titles sported some of the most memorable music in their series. And to this day, they're still having some trouble topping that with their current games.
4) In both storylines, there exists a corporation that is involved with bioengineering: DOATEC and Judgment 6 (aka J6). They both have used ninjas as test subjects for creating bioweapons. In DOA it was Kasumi who was the successful test subject, codenamed "Alpha". In VF, it was Kage-maru's mother, codenamed "Dural". Kage-maru may find common ground with the ninjas of DOA to eliminate the threats, should they ever converge to bring about the end of the world.
5) As of Virtua Fighter 5 R, Hitomi may find an interesting match in Jean Kujo, as Ein has regained his memories as Hayate. However, Jean Kujo is an assassin for J6 and may not share the same sentiments. Either way, it would make an interesting fight, as they both share aspects of Karate.
6) Christie and Sarah Bryant. A femme-fatale assassin of DOATEC vs. a former brainwashed femme-fatale assassin of J6. Their obsession with their respective counterparts - Helena and Jacky - is what drove them to keep fighting.
7) Bass Armstrong and Jeffry McWild are not only devastating grapplers and have high damaging simple strings, they also compete in their respective tournies to pursue their personal dreams: Bass wants to take up motorsports, and Jeffry wants to be a renowned fisherman.
8 ) Zack and Brad Burns are not only experts at Muay Thai, they have a high sense of charisma and are natural playboys.
9) Tina Armstrong versus Wolf Hawkfield. The battle of the sexes. The most popular female wrestler in the U.S. versus the most popular male wrestler in Canada. Both have similar moves and a giant swing to boot!
10) Jacky Bryant and Jann Lee are both seasoned Jeet Kune Do practitioners, each with a different battle cry.
11) Pai Chan and Lei Fang are not only elegant and refined, it's also debatable that they both were the first to use specialized defensive holds. While Pai was the first character to have defensive holds in the series, Lei Fang may have been the first to have advanced holds.
12) Bayman and Goh Hibagami are both professional assassins, and badass ones at that. As a plus, Goh has at least one thing in common with Christie: They both love diamonds.
13) Kokoro works two ways. With Aoi Umenokouji, they both want to pursue martial arts while maintaining their peaceful occupation. With Akira Yuki, they share some similarities in their fighting styles.
14) Like Gen Fu, Lau Chan doesn't have long to live, and is looking for a worthy successor to his deadly kung fu. Lau may have a clearer understanding of the right person when he sees Eliot and how Gen Fu has raised him.
15) Lion Rafale and Helena Douglas. They're not only French, but Lion may spark an interest in Helena because of their common rebellious nature toward their respective fathers' foundations and wanting to be freed from their cage, so to speak, but Helena might be turned off by him because his fighting style reminds her of Christie, her mother's killer.
16) Brad Wong and Shun Di are both drunken kung fu practitioners. Because Brad Wong is much younger, Shun may mistaken Brad Wong for his long lost student he's been looking for ever since the second VF tournament.
17) Eliot and Eileen based on cuteness factor alone would make them a great pair. They may also be the youngest of their bunch.
18) La Mariposa and El Blaze: Two Lucha Libre wrestlers, each with something of a rivalry with a fellow wrestler,Tina and Wolf, respectively. What more do you want?
19) Bayman also has a common past with Vanessa Lewis. They have both had their parents killed when they were little, and were taken in to be trained as weapons. They also had the irony of ending up destroying the corporations which were once their benefactors.