I heard all that stuff is privately owned. Bloomberg can’t touch it.
Assuming that Bloomberg actually believes in private property rights, you are correct.
HOWEVER, the generators and supplies aren't there out of the kindness of the owners hearts. They are there because a contract is being fulfilled. Since there is a need for them elsewhere, and these are currently available, it would be trivial to contact the owners and get a contract in place so they could be used for those in need.
There is nothing stopping him from renting them.
In fact, they were being rented for the event and I’m sure the owners would love the revenue.