RE: Posting non-Steam deals here.
1) If it's a non-Steam Steamworks game deal, there's absolutely no problem posting it here. In fact, please do. Steamworks = Steam = this thread.
2) If it's a non-Steam game deal that isn't Steamworks, use your own discretion. There's no problem with the occasional person popping in and posting really good non-Steam deals (particularly if it's something that very rarely goes on sale), but if you're making a habit of it it might be good to revive that other thread or consider starting a dedicated thread for the service you're posting for.
3) If it's a GOG deal (since GOG already has an active thread) probably don't post it in here unless someone is specifically soliciting feedback on a game and the GOG version is cheaper. Same goes for any service that has its own current thread.
It's no big deal, no one is going to get banned for posting non-Steam stuff, just a little bit of housekeeping