Some videos, soft penis, held dog... are plain bad.
If the dog is hard and the other partner is careful it should not be very differend from holding the knot on the hand and pleasing orally.
In this late case I' d class it like peanut butter baiting. No harm done, fine if someone want to have a try, but certainly not something I'd want to be sering used in porn.
(in fact, when comercial porn flics are involved it is usually the first case, forced because they need "action" )