Im with the group that does NOT hook up the black tank flush hose until I need it.. And then I disconnect when finished. I don't want there to be any confusion at all, even though I have two different color hoses. White for potable normal use and black for black tank flushing.
While I will readily admit I am new to RVing, my assumption is that campgrounds can, and might do something Im not expecting to my personal camp space. Any time I am away, I turn off the water. When I return, I turn the water back on, and double check everything. If I turned the water ON, and there was no water flow, I would not turn the main on without checking with the campground first. Never know why they turned it off. If I saw something untoward, I would check first.
I've already had the grounds maintenance people knock my cord loose from the pedestal when edging... so I always check that too.
I assume I am renting something and that the owner may do something Im not aware of. If I was staying at a hotel, and the water was turned off at the toilet, I probably wouldn't turn it on without double checking with the front desk either.
I do hope you get a satisfactory resolution. Please do keep us informed on how it goes if you don't mind.
Mike