Can CiviRules add a contact to an event?
Not at present - I've investigated this myself in the past.  You can find a complete list of actions in their repository (though of course other extensions add actions).

I considered writing the action but it turned out to be complex.  A rule that adds everyone to a pre-determined event is easy enough - but creating a UI that could handle actions like "Add contact to the next workshop" proved trickier and not worth the effort (for me, YMMV).