I think it's putting the horse before the cart to send out an AAA title to be developed by 2 guys at NEC with no previous working knowledge of the game. It's far more likely the other way around, plus the fact that Capcom can keep their precious source code close to their chest.
Have you seen how many platforms have Street Fighter II ports, and how much money many of those home ports made? That source code wasn't precious at all. That source code was the town whore ; )
As you yourself said, there are several names with no other credits, and they could well have been NEC employees, especially if they're not listed for the ports to other platforms.
As for 2 guys porting the code for an AAA title, I don't see how that would be impossible at all. 2 qualified, experienced coders working salaried, long-hours work weeks with all the assets and program structure already created, with design documents already prepared for dealing with ports, porting it to the PCE and then optimizing the code. And one of those un-named folks probably did the music conversion. No, that's no problem at all. Keep in mind that at that time in game development, AAA titles could be crafted by one or two people, even if they usually weren't. I don't have a problem buying into 2 programmers handling all the code-porting duties.
Again, they probably had some guidance and consulted with Capcom, but I doubt Capcom actually had to touch any of the code on the port. The PCE was simply not a platform of expertise or interest for them. It would be much easier for Capcom to leave the port to NEC Avenue since NEC had the programmers who know the hardware. Look how many other Capcom ports they did. They probably had a good working relationship with the NEC Avenue team and trusted them to do the coding.