The surgeons that I work with are completely crazy about sterility when it comes to a THR more than any other procedure because you are taking an implant and putting it into a major bone within the body that produces important cells for the body. We literally bleach the whole OR down from ceiling to floor, take everything out, bleach anything that will need to go back in from top to bottom, make brand new scrub and alcohol for the patient, we aren't allowed to use anything to keep them warm that potentially could blow things around (normally we can use a bair hugger that uses warm air to help keep a patient warm). They culture the site at the time of surgery, are super cautious about things being sterile and having implants on hand for the procedure that were ordered close to the procedure to ensure the best sterility. It is not something that should be waved off.
I even was recommended to have my dog have a dental a month or so pre-op to ensure any bacteria that could be slipping in via the gums to be taken care of.
I was very careful afterward, but the stinker managed to lick some at her sutures. They got a bit red and the vet decided that giving her antibiotics then would be a good idea. It isn't the amount of the drug or the times that you give the drug that indicate how serious of a drug it is. It is more the actual antibiotic class and what the drug covers in what it can take care of. The drug of choice for most orthopedic procedures (human or animal) is cephalexin. Most dogs will end up getting a gram of it twice daily post op. But there are other stronger drugs based on what class they are in and what they can penetrate. If they start talking IV antibiotics, then you can be more worried there.
If they worry about implant failure due to infection, they will remove it and culture the hardware/area it was removed from.
Speaking from experience, when I noticed that Kenai's incision was a little redder than usual while at one of her acupuncture appointments, I mentioned it to the main surgeon for it and he hadn't thought much of it, and just gave an antibiotic to cover just in case. There was never a sign of trouble on the radiographs however. How old is your dog? I think the only time that we ever removed a THR implant was a dog who ended up with osteosarcoma, was very, very old on top of it all. Otherwise we haven't had issues.
However I only know my surgeons, and we're out in Idaho.
It would not hurt to perhaps ask for the surgeon to call and express your concerns, ask him what is happening and why he was not as concerned. There may be a reason for it that you and the person whom you spoke with are not aware of. Not all vets are of the same making, however the ones who went through extra training/residencies and had to pass yet another exam and set of requirements you would hope were a little more up to speed than others.
Hope everything turns out okay for you guys.