Technically the bees don't cause much damage. They will do things like remove insulation. Fermented honey, moisture, ants, wax moths, etc are all more damaging but technically a result of the bees. At least in an observation hive you can see what's happening before it spreads.

If the space is sealed, how would they get into the walls?

Carpenter bees tunnel into wood.

An interior space like this could easily be lined with a more durable material. They also would be easily observed, and wouldn't occupy the space if a queen has taken residence, even if it did it would be quickly crowded out.

Carpenter bees wouldn’t be hanging out with honey bees.