Stacker's Outbox offers similar functionality to Buffer(scheduling,timezone targeting etc). Stacker additionally pulls together all Comments, @replies and @mentions from your Facebook and Twitter accounts into a single universal Inbox so that you can Reply from one place.
I'm not aware of such a rule. I think thats a bit of a grey area. As long as you are adding value to the network and not being a spammy-bot I dont think they will have an issue here.