You are allowed to paddle in order to avoid danger. As in under a bridge with adverse current. Also if in front of a commercial vessel, like a bardge in no wind and need to get out of the way. It does state that you can not paddle to advance your position in terms of competitors. So basically yes, unless you get carried away and it is obvious your are not just avoiding danger.
I believe the Mug Race rules also allow you to accept assistance to right the boat etc. and still continue racing.