You don't "need" GPU in that CPU alone can produce a render of identical quality as GPU. HOWEVER, GPU, i.e. Iray/Nvidia renders much faster than CPU which is why we "want" to render in Iray/GPU. Keep in mind that there are no consumer grade CPU farms. We only have single CPU machines and the most powerful consumer CPU today probably cannot render Daz faster than a GTX970 from 5 years ago. The caveat is that you can have 64GB of DRAM cheaply with CPU rendering. If you want a scene with 50 G8 characters instead of the one G8 that 4GB GTX970 will fit, Nvidia charges 20x more for professional cards with more VRAM that have similar processing power as consumer cards. Some professional render farms use server grade CPU only as it is more flexible of tools they can deployed and they are not locked into proprietary GPU technologies to be gauged later.So you are saying that if you had a computer with a super powerful CPU and a good amount of DRAM that would be all that you need. No need to have a super powerful Graphics card. because Daz3D would render everything only using the CPU?
For Daz, GPU rendering is just Nvidia as Iray is Nvidia's technology so buying AMD graphics card is useless as far as Daz3D is concerned because you will be rendering in CPU. Again, the quality of the render is the same regardless of CPU or Nvidia Iray.