Agreed NOT to tie the horse when vacuuming.
I have a narrow aisleway, so I don't even halter my guys.
I use the shop vac with soft brush attachments.
Never vacuum the family jewels, unless you want plastic surgery for yourself (no I didn't do that, it's just good common sense
Two of my horses love their faces massaged with soft brush attachment, two get wild-eyed and say "not on your grandma's tintype"
Legs can sometimes be an issue for certain horses. Horses are flight animals so sometimes the sucking sensation of the vaccuum can give them heart failure. My Arab used to be that way but I worked him out of that.
I love the shop vac in the winter months because I can't brush four horses good enough to get all the dander up. I'm old, short and my shoulders hurt from doing this stuff all my life. I am all for any piece of equipment that will make my barn life easier and get the job done without killing someone