Yep! For the Steam version, select the "PC" platform when you go to submit a run.
Generally, the official emulators aren't that great for speedrunning. Steam Game room is particularly notorious for lots of input lag, along with the audio being off. Buying the game on Steam gives you access to the roms that you can use in retroarch or fusion, and for most of preferred over using Steam.
No, the only unofficial emulators allowed are Genesis Plus GX (via Retroarch normally), and Fusion.
In addition to the previous news post about extra IL variables that allow runners to submit runs that start Act 2 with glitches, shields etc from Act 1, we have decided to remove the Legacy Ruleset, to do this we have grandfathered any runs that adhered to the current ruleset and just don't meet the