AND yes human hospitals do use a sealed type {laymens term)of procedure when extracting cancerous tumors that the veterinary industry does not use. I was informed of this it by qualified professionals at two different Universities.
If your are talking about the sterile adhesive drape commonly used in human medicine, you are correct that it isn't commonly used in veterinary surgery. BUT it has nothing to do with air coming in contact with tumors, just general infection control during surgery.
Fortunately, aside from horses, the species we do surgery on are not terribly susceptible to tetanus and peritonitis.
Imagine the costs of elective surgery if we instituted those procedures when not entirely necessary.
My point was that the assertion that exposing tumors to air leads to more tumors, worse tumors, metastasis is just wrong.