The 31-year-old is in line to feature for the Toffees in Sunday afternoon's Premier League meeting, two months after swapping clubs on a free contract.
Rooney spent 13 years at United and departed as the club's all-time record scorer, and Giggs sees no problem with his former teammate celebrating should he bag a goal for the Toffees at the Theatre of Dreams.
"If you score a goal, you hear players talk about, you sort of lose yourself and I don't think we should get away from that," he told Sky Sports News. "Show respect, don't go over the top, but if you score a goal then celebrate. I think fans recognise that.
"Knowing Wayne, I'm sure he'll be nervous, but relishing the chance as well and he'll want to score because that's his job. He'll get a great reception from the United fans because he was such a great player for United in such a successful era as well.
"I'm sure he'll be looking forward to it and the United fans will be looking forward to seeing how he does as well, hoping he doesn't score and Wayne the opposite, hoping he does score."
Rooney won five Premier League titles during his time at United, plus each of the Champions League, Europa League and FA Cup.