Occasionally you can, but it comes with caveats, even for PhysX:
• Only works on Windows
• Only works with Nvidia graphics cards (and only them, cheap nvidia card for physx + AMD card for graphics will disable PhysX)
• Not guaranteed to be faster for all cases, needs to be evaluated on a case-by-case basis
So even if the physics engine can, not all game engines use it. The Unity devs e.g. stated that they won't bother with it, as the limitations make it unattractive to pour effort into.
• Only works on Windows
• Only works with Nvidia graphics cards (and only them, cheap nvidia card for physx + AMD card for graphics will disable PhysX)
• Not guaranteed to be faster for all cases, needs to be evaluated on a case-by-case basis
So even if the physics engine can, not all game engines use it. The Unity devs e.g. stated that they won't bother with it, as the limitations make it unattractive to pour effort into.