The hole is where the drain came out? Maybe the size of a dime or a nickel? It should heal up REALLY fast, within 2 days. I assume the area is clipped and they were probably given a bottle of nolvasan and told to hot compress? I’d do that until the hole closes, just so you’re sure that everythings draining properly.
Re: the attack. Given the description, I’d sure as hell report that. If for no other reason than the dog owners take it seriously and I don’t know- keep their dog on a leash and get some training help?
The laws regarding reporting bites are totally different in each state so unless you are from ME you cannot make a statement of the vet’s behavior. In MA, there are very specific laws regarding when to report and not report a bite, and unless the biting animal’s rabies status is confirmed, there are very specific laws regarding lengths of time for a quarantine for the bitten animal.