Its not dangerous to run with a split cv boot, it will just get water and road muck in the actual universal joint and will seriously shorten its lifespan. You fail and mot with a split cv boot, so best to get fixed soonest.
Colins motor with the creak on it needs lookin at, you didnt say if it happens when you are trickling back and forth or stationary. My mates 172 creaked at parking speed and his offside upper supension bush had collapsed, dealer reckoned it had been assembled wrong. Should be no problem with warranty on any driveline component, it is a safety item and should be treated as urgent by the dealer.