Are you saying that because Bashir calls him "Fontaine," that he doesn't carry the first name "Vic"?
Could be. In the regular universe, we don't know Felix's last name, after all.

I know I've stated this theory many times, but I'd just like to repeat it now. The way I see it, Felix of the regular universe is a Dilbert-like cubicle drone who created Vic as a way to live out his fantasies of being a 60's-era Vegas lounge singer. And as is normal for holo-programmers, Felix used his own physical appearance as a model for Vic.
In the mirror universe, on the other hand, Felix gets to be the badass warrior that his regular universe counterpart can only dream of being. Of course when Rom first meets the "mirror Fontaine", Rom immediately assumes it's Vic, but that's understandable since I'm just guessing that Rom has never met the regular universe Felix. Rom HAS, however, met his own universe's Vic (at least I'm guessing he has, as Vic is well known to the inhabitants of DS9), so that influences his judgment, as it were.
Now I hate to toot my own horn here, but let's be honest - what is more likely? A ragtag band of Terran rebels somehow managing to construct an android which looks, thinks and acts indistinguishable from a human being (Noonien Soong is, AFAIK, the only human in history who ever managed such a thing, and of course we never see the "mirror Soong" here)...or the mirror Fontaine simply being the counterpart of the programmer who created Vic?
Actually, I do remember reading that it was James Darren's idea to have there be a "mirror Fontaine" in the first place - he just wanted an excuse to be a fighter and charge into a scene with guns blazing. So I guess that's the end of it.
