This. If you want to stream any game that's not on your steam account to the steamlink you need to add them to steam first.
Im also pretty sure the is a way to steam you're desktop to steamlink so maybe that would be another option to launch non steam games without using any 3rd party software.
Ok I've figured out how to get my Origin and Xbox games to play, via that UWPhook, but one problem I'm still having is my xbox one controller. It is bluetooth hooked up to my steamlink, works properly on any Steam games, but doesn't seem to want to work with the xbox or origins games on the TV via steamlink.
I've come so close to getting this to work without having to buy a massive, in the way, $200 or more xbox! I don't want to fail now lol.