At the moment there are no server driver for your FirePro S7150 and that's why some features may not work for you. At the moment the OS that are supported are Windows 10-64bit and 7-64bit, Linux and ESXi 6.5 and 6.0
So, a passthrough GPU designed for multi-user access via VDI or RDS, ie server roles, doesn't have a server driver for Microsoft's server O/S? That just sounds plain wrong. Dell do have a driver, but it's very old (dating from beginning of 2016), but that didn't make any other difference either when trying that.
I then thought, well, let's try Server 2016. I upgraded the box from 2012 R2, then installed the 'Enterprise' Win10 x64 driver (certified for mxGPU). All this went ok. On running dxdiag again, I can now see the correct Feature Levels and Driver Model (WDDM 2.1, DX12 etc),but DirectDraw Acceleration and AGP texture compression are *still* not available. <sigh>
No idea. Very, very odd.