An English question: Can you call a boarding house a "creep joint"?

Some boarding houses could be "creep joints".  Not all creep joints are boarding houses, and not all boarding houses are creep joints.  So, sure, you "can" call a boarding house a creep joint.  Not sure if it fits or not.  It depends on the particular boarding house.

You can call it whatever you want.

Spank my butt & call me Judy.

Sure, especially if it only says it's a boarding house but it's really just a flophouse used by addicts to trip and whores turning tricks, any of whom would rob you blind as soon as look at you. It's kind of like all those rub-and-tugs that call themselves massage parlors to try and fly under the radar of the law but are really just whore houses.