After the farce with the ESRB adding and then removing the listing for Vice City Stories PS2 version, we now have much more definitive information which essentially confirms the title's existence.
A search on playstation.com
for "Vice City Stories" now reveals a PlayStation 2 port of the game, the more detailed page can be found here
. Note the fact it now has a SLUS number, a unique number Sony give to each game they certify.
Rockstar don't comment on "rumours and speculation", so we will have to wait for an official press release from Take Two to confirm the title, it can't be too long until we get one - more and more of the larger gaming sites have picked up on the ESRB article and have reported on it so it's pretty well known already.