This was different in the first version, but DLSS is now just a thing a developer needs to "turn on" in the engine. However, the feature will only be added to the Unity engine with the 2021.2 version, which is suposed to come end of the year. VaM will need to update to that Unity version, so this will only happen with VaM 2.x.
FFX should be similar, it needs to be supported by Unity first, then VaM needs to update to that Unity version.
I think DLSS should give better results, for a while. But its not impossible that AMD can catch up eventually with some magic of their own. However, right now they are trying to reproduce Nvidia's resolutionary AI approach using traditional upscaling filters. We have seen the crappy results of the tranditional filters for years in all kinds of 4K TVs and console games claiming to run at "4K", not sure AMD can do that much better using that approach. But yeah, we have to wait and see, I'm sure there are smart people working on both sides