Yes, I used to take them together just for fun and I was lucky enough to not have a problem. I’m talking about 20 mg of Percocet and 6 mg of Xanax (4 percs & 3 Xanax at 2 mg). I wouldn’t ever recommend doing what I did, but one of each 12 hours apart is plenty safe.
I would be careful about combining them even if just because getting into that habit leads to feeling like you don't get the full effect without both. Bad habit to pick up.
But taking 5mg oxy in the morning and I'm guessing 10mg diazepam in the evening is fine.