Localization To The Rescue: Did anyone expect Tatsunoko vs. Capcom to be localized and published in North America? Capcom USA deserves a big thanks for going through enough Licensing Hell to pull this off.
Marth Debuted in Smash Bros.: Surprisingly, and as far as America goes, Ippatsuman is the only Tatsunoko character to fall in this trope. To recap on the others: Gatchaman was brought over too many times to countnote The most important ones being Battle of the Planets, G-Force: Guardians of Space and Eagle Riders, Casshan and Polimar had their 90's OVAs licensed, Yatterman debuted in America as Takashi Miike's Live-Action Adaptation for a limited theatrical run, Tekkaman the Space Knight got an extremely campy dub, Gold Lightan's toys were/are available internationally, Karas received a proper DVD release, Tekkaman Blade became Teknoman, and Hakushon Daimao is now a non-entity. The same can even be said for the European countries, as nearly every Tatsunoko anime was dubbed there save for a few (like Ippatsuman).
Hakushon Daimao actually had a brief television run in the US (courtesy of Saban) as Bob in a Bottle. Still, other than the cast of Gatchaman, nearly all of the Tastunoko characters are extremely obscure in the West.
No Export for You: Successfully and surprisingly defied, as unlike nearly all anime crossover game developpers, Capcom went out of their path to personally deal with the featured anime's international licensees (That, and they were Pandering to the Base). If you wanna get technical though, it's only the Updated Re-releaseUltimate All Stars that made the cross overseas; the original version (Cross Generation of Heroes) is still locked to Japan. note This is only significant when concerning Hakushon Daimaoh, who'll remain exclusive to that version, as well as the character-specific songs (which are replaced by generic BGM for the stages). But otherwise, no biggie. Besides, we get Tekkaman Blade, Frank West, Zero, Joe Asakura, and Yatterman-2 a.k.a. Ai-chan. Funnily enough, Japan wasn't supposed to get the re-released version. However, thanks to the fans wanting it, as well as the development team asking for it, Capcom decided to release Ultimate All-Stars in Japan as well.
Even funnier is the fact that Phoenix Wright was not included BECAUSE the game was going to be translated. He would have attacked with his Catch Phrase in a word bubble. The problem being is that due to the words "Igiari!" (the japanese version) and OBJECTION! (the american version) being so different in length, they would have had to change the size of the speech bubble, resulting in an unavoidable American-sized attack. Because of this, they couldn't include other characters from the series, Franziska in particular who would have used her whip.
Frank West's VA isn't the same one in his game. Coincidentally, Peter von Gomm voiced X in Mega Man X7.
The same applies to a good portion of the Tatsunoko characters. Casshern, Polymar, and Ippatsuman are respectively voiced by Daisuke Ono, Kunihiko Yasui, and Masayuki Kato instead of the original seiyuu or the seiyuu from the various OVAs.
In the case of Viewtiful Joe, while there was no English localization (and thus no Dee Bradley Baker), Tomokazu Seki (his seiyuu from the anime) did not reprise the role of Joe (instead, he was voiced by Shinji Kawada).
Shown Their Work: If you only knew that a lot of people in Capcom's (Japanese) offices were Tatsunoko fans (as Seth even explained, their accountants squealed when they saw Yatterman-1). In fact, the games have so much stuff in it that gives various references to its old shows. In fact, this blog shows how much dedicated the team was when making the characters.
Toshiyuki Morikawaclosely averts this it in Ultimate All Stars. He has voiced Ryu in all the past games and also voiced Tekkaman Blade himself, but Hiroki Takahashi took over as the voice of TvC Ryu by virtue of Street Fighter IV.
What Could Have Been: Phoenix Wright and Franziska von Karma were intended to be in the games. While the latter wouldn't have been hard to put in due to her whip, The developers had trouble with Phoenix. Though it is understandable why - especially since the game would feature worldwide match-up, and having two versions of his attack (Objection!/Igiari!) would really be screwy. A developer once mentioned that adding Phoenix Wright to the American version would have been a game breaker- almost literally. "Objection" would have added a few more hits (OB JE CT IO N!) to his attack compared to "IGIARI!" from the Japanese version. Not only would this have made him too powerful, but would have been hard to program. They eventually settled for a different implementation of "Objection" (in a single unbroken word) to make Phoenix work in UltimateMarvel vs. Capcom 3.
This page lists all the other characters who were cut from Cross Generation of Heroes. The fun bit is that Joe The Condor and Yatterman-2 were the only ones who made the cut over that list for UAS.