My regular occupation is emergency generator systems, all sizes, mostly commercial. Was at a residential last week doing a routine and the home owner mentioned bees, had my interest right away. He pointed out where bees were coming and going, looked like a large and very active hive, about 30' up near the top of a rock chimney. From what I saw, they were coming and going in a hole/crack about 5' from the top. Think they were in a void in the rock, not in the area that passes the smoke. He mentioned that a couple of bee keepers, one of which I know well, had came by and took a pass, advised him to get an exterminator. I mentioned that I liked honey and went back to the generator. That would be a tough one, not sure how one would get them out of the chimney, not to even think about trying to do that off of a ladder. Some you have to just pass up. If it were me, I'd probably leave the original hive right were it was at, kind of leave it for seed, and be sure to have a few swarm traps out every spring to catch what I could.
Yes, good idea to have a hold harmless waiver before starting anything. Might even have a liar, err, I mean lawyer take a look at it before using it.