Comment by chuckadams

Yes, it's routine to hire background-checked cleaning crew, and some higher-security operations even require the company to put up an extra bond. One only needs a clean enough record, but I've known a few people in housekeeping with old drug convictions who still had no problem working in secure areas at defense contractors. When they would go into the secure area, there would literally be a flashing light with someone loudly announcing "INSECURE!", and everyone working there would lock their screens and basically go on coffee break. Obviously not a thing a server room has to do, but those have cameras watching the every move of the cleaner, the racks are in locked cages, and the cleaner has to leave any electronic devices they have in a bin at the door. It's not like they search them thoroughly, but there are severe consequences for getting caught, and they don't have or need much time to clean the server rooms anyway, let alone get away with espionage.

There's still a lot of mischief you could pull off with a cleaning crew, but facilities maintenance beyond housekeeping has a lot more opportunities.