1. Viewport acceleration is about the only thing that actually "requires" hardware acceleration. Now, there is an option to use OpenGL Acceleration for ShadowMaps in MentalRay (in Maya), and in older versions of Maya - some particle effects had to be hardware rendered and composited back into the scene (and still can be for particular cases), but for most intents and purposes, your rendering can be accomplished entirely in software and depends solely on CPU and memory.
2. There are a few hardware dependent renderers on the market (mostly targeted at the gaming industry) such as CgFX/Gelato, DirectX/HLSL, and it looks likely MentalRay will start to get some hardware acceleration in the near-future since nVidia bought them up. nVidia also supports physics calculations on their upper end cards (I believe a group has also achieved this on ATI cards)
3. Sorry, I don't understand the question on this one...