Quake 2 Model Legality

Would it be legal to use the standard Quake 2 models in a GZdoom project? I would like to use them because they are good looking and already in MD2 format.

It's kind of a gray area. Many popular Doom mods use other id game resources. Just make a disclaimer and go about your project.

It's not legal but it's kind of done a lot and your not making money off it so...

It's about as legal as importing Metallica MIDIs as your soundtrack.
i.e. Slightly not, but people do it anyway.

From a legal standpoint, probably not advisable, but yes, people tend to do it anyway. From a community standpoint, yes, people do already do this sort of thing (the ZDoom hub "Temple of the Ancients" makes liberal use of Quake 2 and Hexen 2 resources, for example), but then there's the extremely vocal minority that will loudly dismiss any project that does such things.

Basically, at this point, it's more of a choose-your-fate situation.