The drivers WTWF is complaining about don't work on WindowsRT, 8.1 or not. The whole "Windows 8.1" thing is a red herring. The reason the drivers don't work on WindowsRT is because only Microsoft signed drivers will load on WindowsRT (this is a policy that can't be turned off, and affects only the tablets, not the PC editions of Windows). They didn't load on WindowsRT with 8 and they won't load on WindowsRT with 8.1.
And no, the drivers WTWF is talking about aren't Microsoft signed drivers because Microsoft doesn't make NICs. They are probsbly Broadcom/Verisign signed, not Microsoft/Microsoft or Broadcom/Microsoft signed, hence why they don't load on the MicrosoftPad.