How does that work? If I buy a 2080 Ti and then decide to use it in an internet-hosted box that I rent out to other people, the first-sale doctrine should tell Nvidia to piss off if they have a problem with it.
Also the consumer cards have artificially small memory sizes (e.g. 11GB max) which painfully constrains DL jobs.
No manufacturer is allowed to build Tesla-like cards. Theoretically AMD could crush the nVidia profit margins by releasing cheap data center boards, but their developer support is rubbish and they want that high margin cash too.
In that context, the Mac Pro doesn't sound too bad a proposition. I say that as someone who recently built a dual-Titan/AMD Ryzen system, and while the pain of the build is almost gone away .. I do lust after that sexy Apple box, being plug 'n play and all ..
Apple can't really compete except in mobile GPUs, which is all about power constraints set to single digits Watts, vs >100W for server. That isn't all bad for Apple, there is lots of inference to be done, but by refusing nVidia hardware they impose a developer hurdle.
I'm looking forward to people putting 2080s into the new Mac Pro and seeing how reliable it is.
As for nVidia banning it, if you've the cash you can buy cards, just becomes painful. nVidia were doing it more because the GPGPU demand was choking the supply to graphics customers, and later dumping obsolete (for crunching) cards on the market en masse, interfering with the mid-tier card sales channel.
Edit: You may also need the official Nvidia driver. I have never run anything with the OSS drivers.