Multiple Libraries

yes.

Yes, in fact it's almost a standard practice. It is nothing unusual for a single project to use DirectX/OpenGL to provide access to graphics hardware, an abstraction layer like Allegro/SDL/Ogre3D/Crystal Space/etc to simplify interaction with the graphics API and windowing API, OpenAL/FMod/etc for sound, Newton/ColDet/etc for collisions, etc etc etc. You get the idea.

In general just make sure you know what any given library is intended for and don't use libraries that perform conflicting tasks. For example you can provide both DirectX- and OpenGL-based rendering for a game but you generally wouldn't allow both to be used at any given time.