If the overall+shirt suit is real, I think it's very probable that the shirtless one is a "panty-variant" of it (just like you can remove Christie's bra when you select her C1 costume with Y).
Couple of interesting notes about it:
1) That render is definitely not in-game. The skin shader and the hair are completely wrong. It is possible, however, that it's a screen-cap from one of the artists from within 3DS or Maya or whatever.
2) That variant of the overalls is not the one from DOAU. The legs on it are shorts, as they were in DOA1. In DOAU they were full length.
3) The texture work looks different between the two shots, with the in-game one being notably higher res, and the actual texture-work is different.
I'll be interested to see if it's real or not. If it is, it will be a full costume variant, not a button-switch. I feel sure of that.