The drivers for AMD, Nvidia, and Intel video chips - at least those used/supplied/supported by Apple are written by Apple and included in the Mac operating system. These might get updated when Apple update the operating system.
AMD and Intel do not themselves write drivers for the Mac video chips even if they make the actual chips. Nvidia however does also write their own Mac drivers. In fact Nvidia also makes drivers for some cards Apple do not themselves support e.g. the GTX-980 and 980Ti.
There is a fairly widely held opinion that Apple's drivers while they work are mediocre in terms of performance as a result the Nvidia drivers for the Mac are considered superior to Apple's own drivers. Furthermore sometimes Apple also wilfully omit certain features that certain video cards/chips are capable of, for example Apple do not support audio over HDMI on some Mac Pro PCIe video cards, and Apple also do not support 30bit color aka 'deep color' on some video cards/chips. This is despite the fact the cards can do these functions and even do it in a Mac when running Windows via Boot Camp. 😮
There is nothing forcing Apple to (fully) support cards they never sold or shipped but it is annoying, especially if it is an AMD card for which there are no alternative AMD drivers. 😟
I find all this particular bizarre considering the number of job posts Apple have and do post for Mac graphics driver developers. You would think an infinite number of monkeys could come up with better drivers. 😝
