You mean with the cracked drivers, you'd probably get lower frame rates but it should do alright, unless its a very cpu intensive game as it is, then it might chug overall I wouldn't suggest it, physx is overated
These are two different things:
1) Hybrid PhysX with an AMD primary card that uses a secondary Nvidia cards for dedicated PhysX. That has not been supported by any drivers over the past two years.
2) What I gather from the original post is, can you do PhysX on the CPU using standalone PhysX drivers. This is unnecessary and won't work. You can run PhysX, slowly, off the CPU without additional drivers, just using game's already embedded code. The PhysX drivers are for the Nvidia GPU and won't translate to CPU instructions.