Yes, you can still run on emulator, but your runs will be rejected if you submit them. Because of emulator inconsistencies and how easy it would be to mod the game, emulators are banned. It's still possible to mod the game on ps3 and xbox360, but it's a much longer process to do that and most people don't understand how it works. The few that do are modding multiplayer and have no interest in speedrunning.
Basically, if you want to run the game on emu, we won't stop you. But your runs aren't allowed on the boards.
Yes, the long awaited PC version of Red Dead Redemption is coming on the 29th October. Upon the release, there will be a 30 day leaderboard embargo period that allows me and anyone that is remotely interested in this game time to establish rules, strats and glitch hunting/testin