I've never had em cover up a boot, but they've covered up my thermostat wire a bunch of times. Did you use boot rails to put the boots up? If so, I would try getting one of those stud finders that find metal studs & see if it would pick up the boot rail. I've never tried this but it seems like it might work.
Life is like a jar of jalapenos. What you do today might burn your ass tomorrow.
I was at a new construction job about fifteen years ago.I left 1/2 hand bent double hemmed drywall frame on everything that was to be cut around.I was lucky enough to be there when they started drywalling.The bozo's actually smashed my rings flat & covered registers instead of cutting around them.I told the drywall foreman & he oh well I guess you'll just have to find them.I came back with a 26oz.framing hammer.& I said really loud so he could hear.Well Jeff(My helper) I hope it was here or they will have to patch a hole.I took a big swing with the side of my hammer & WHOP!I busted about a four inch round hole with the side of my hammer.My helper laughed his butt off & said Boy you got lucky that time usually You miss Mark!(I knew exactly where it was we were f-ing with them)Thet guy said ok ok ok we will cut them out!!!I scared the heck out of him!Any way I would call the drywaller & tell them it is their responsibilty to cut out around registers & an add will be charged to the job if you have to do his job for him!!