Does BlitzQuake die on CVision/BVision because people try to use features beyond the Permedia2's feature set?
Things to note (I have learned far more about the P2 than I ever wanted to ;-) ):
The Permedia2 does not do chromatic blending. Hence all quake2 style coloured lighting (achieved by multiplictavely blending an RGB texture map in a second pass) will not work.
The Permedia2 does not do MIP mapping. Therefore any minification filtering using MIP maps will not work.
If the engine has been written in an 'assumes the following features' kind of way, rather than properly querying capabilities problems may arise.