Yes, you can still use your "cpu only" with Iray, the same why 3dlight does. However renders will take a bit longer. But there are those who are using cpu only and getting decent times and results. All depends on your scene. The end result in terms of quality will be the same, only time is affected without an nvidia gpu.

In our testing, we have found that, as long as you properly light your scene (Not comparing Headlamp only or no shadow renders in 3Delight.) the average time for Iray renders in CPU mode is about the same as 3Delight., Yes, some things go nuts, but generally it is within +/- 10%.