If you want to do something like acidophilus, get a rabbit specific pre and pro biotics. Human acidophilus only works on humans and species of chimp because were the only ones that have the peroper bacteria in our intestinal tract for it to work on.
It is not necessary for any animal going into surgery to receive this. As long as shes healty now, and eats well before and after the surgery there is no need for the pre/pro biotics.
If the clinic doesn't do alot of small animals the assistants may not know that you dont need to fast small animals. If they do lots of normal surgeries on cats on dogs its habbit to say (no food after 10pm the night before, water is okay... blah blah blah) You can get away with a lighter meal that evening/morning because the pre-meds they give them (usually its the hydro morphone) makes them quite nauseous and in dogs and cats its a great way to get them to vomit up that breakfast their owners still fed them despite being told not to, as well as making them nice and dopey.
I would definatly look into the pain meds, especially surgery on a joint like that, it's quite painful. I can understand none for a spay/neuter because most animals bounce back so fast it's not needed, and that may be another just like the food and water where their so used to cats/dogs (if this was the assistant that told you this) if its the vet.... Second oppinion.
Actually most osteo surgerys are done by specialists... well up here anyway... What is this surgery costing you if you dont mind me asking, I have a feeling this is going to be a situation where you get what you pay for, alot of vets shouldn't be doing specialized surgeries like this and yet they still do. Ahh...
Apologize for any bad spelling (I'm still in bed)