I think its possible its the other way around and Nvidia is the one seeking out partnerships. HZD, God of War and now Spider-Man all support DLSS. Days Gone however, does not. Bend Studio did not rule it out completely, so its possible it was a matter of integrating it with their modified version of UE4. Or, it wasn't worth Nvidia's time or money
MS has always been vocal about their relationship with AMD so I think its either that which keeps their games from getting Nvidia proprietary feature support or engines not supporting DLSS plugin at the time games were released (or any temporal solution in cases like Forza Horizon 5). Its going to depend on a case by case basis though, as Hellblade does support DLSS and Flight Simulator is getting DLSS support this year as well.
Curiously Spider-Man remastered is the first game where we can compare FSR 2.0, DLSS and first party proprietary solution i.e. IGTI (Insomniac's own temporal injection solution). From what I've tested in the game briefly, at similar quality levels, DLSS > FSR 2.0 > IGTI.