I don't know what happens when a landlord hides weapons or something under the floorboards and then rents the place to somebody. Say the people renting the place are on vacation and the police has a warrant (made out to the landlord in this example). Maybe they can go in with the landlord (and, at least in Germany, they also need an independent witness) but are only allowed to search the actual property and not the stuff in it (because the landlord doesn't own the stuff). I don't know. But this kind of renting is well covered by laws (including lots of laws protecting the renters).

"Renting" a VPS (webspace would be a better example) probably isn't defined by any laws. It feels more like user data connected to a (paid) software service. Renting a dedicated server is a different story.