....regardless of what the ownership situation is, I would think that the owner(s) would like to know about any possible wrongdoings being perpetrated on their property.
It still goes back to the consequence is friend can get evicted and a complete stranger is added to your house.
This is not a shared lease where 5 friends all have their name on a lease; each roommate has a lease for her bedroom and a share of the common space. Any advise should really take into account that the consequences can be even worse than a known friend.