I'd like to state that Dungeon Keeper and Stubbs the Zombie are both awesome games. Quantity does not necessarily mean quality.
As far as the "Nazi - Postal dude/Tommy Vercetti" correlation, you have to recognize some of the differences...
Both PD and TV are individuals who, of their own volition, decide to liberate the world of several metric tonnes of fat moronic tourists. Often by blowing them up.
The National Socialist party, on the other hand, oppressed, ostracized, imprisoned and slaughtered innumerable innocents as inhuman scum, due to their unfortunate heritage.
Postal Dude, as he himself has been heard to say, holds no prejudice. He kills everyone equally. His rampages are caused by annoying, stupid people who really just don't need to suck his air anymore.
Tommy Vercetti is not so much malicious as he is acutely myopic. He really just thinks those things are all speedbumps.
In both Postal and GTA, you decide whether or not to kill someone based on how much of an asshole they're being, or how much money they're carrying, or how much blood you think will fly out of them if you hit them with that new SYV you stole. The genocide of Nazi Germany was based around viewing entire groups of people as subhuman animals, that needed to be killed in order to remove their taint from the world.
So while Postal and GTA both encourage independent, entrepreneurial behaviour, a game taken from a Nazi viewpoint would exhibit bigotry.
End comment: Racism is wrong, running over hookers is good business sense.