Hi Christa,
It's important for the body to be on as little prednisone as possible for any surgery. Decreases the risk of infection. HOWEVER, once the surgery is over and he's in a stable state and recovering nicely, his prednisone should be increased to DOUBLE his normal dose. This will keep him from going into a lupus flare up.
So yes, you are wise to think this is not a good plan for him. I would talk to his rheumatologist about all this and make sure that once he's past the critical stages of the surgery, he should be boosted to a theraputic level. If he was on 7.5 before, he should be taking about 15mg for a while, then taper very slowly back to his 7.5mg.
I'm not a doc! But that is what has been told to me, if I were to ever need surgery of any kind. I hope this helps!
Ginny