I'm sure they will allow that. But even if they didn't they themselves could host such events anyway.
I'm not sure about how a host can match players probably the players competing will befriend each other and have 1 on 1 matches with each other with both screens shown to the audience (if they don't add spectating mode).
Will it be possible to set up our own regional tournaments, where the tounament hosts will be able to match individuals against each other?
As far as I know right now you can only challenge a friend or be placed in a game by the matchmaking queue. But esports was defiantly a topic of interest and I think that something like that could be implemented post launch along with a spectator mode.