I have been giving this some thought!!
In the first examples I think you are correct, but if you are insured for groundsmaintenance and you completely sub out the tree work-are YOU insured to sub out tree work?? Would you be insured to sub out satelite installation or anything else you chose that you didn't fully understand?
In the example in the fourth paragraph above, I think it is still a grey area but I hear what you are saying. The guy is offering a complete service and his own rigging gear and insurance.
Whos on the other end of the riggign line?? That person has responsibility for the lowered sections and the climbers safety (not letting run/ swing backs etc). If the guy provided his own groundy then the area is less grey......but, what if his guy is busy lowerign and your guys allow a perosn or car into the work area which gets hit then its your responsibilty agian.
Another problem is that you would still need to check all the tickets etc. Anyone can get insurance, that doesn't make it valid. And unless YOU are qualified to carry out all the work, how can you be qualified to check tickets etc?
Another example: A grounds maintenance company "subs out" a rigging job to me and they clear up. I tell them I'm insured and show them climbing tickets and insurance certificate. I don't show them a rigging ticket or loler tickets because they don't know such things exist and don't ask for them and for the purposes of this example I haven't got them!
I damage a load of property and my insurance isn't worth the paper its printed on. The groundmaintenance company try and claim on their insurance and there is no chance cos they shouldn't have been doing that kind of work.
Do you see where I am coming from?? I'm not suggesting you have done anything wrong, just made up scenarios.
There is very little "grey areas" where insurance companies are concerned. They will or won't pay out, there is no maybe pay outs.