I think you have part of that backwards. UDH is compatible with any groupset (including LTWOO), Red XPLR and Transmission are ONLY compatible with UDH. Not non-compatible.
I was talking about a UDH
hanger; you’re right if defining “UDH” as the frame specifications (which is what SRAM does, so I suppose you’re more correct than me) - but if OP has a UDH hanger in hand, wondering about a groupset that is not Full Mount, then there’s not much of a distinction to be made.