It's still a shame they couldn't find some way to do it even if it meant a new VA, especially since Marth and Roy finally got English voices.
I mean, what's he expecting? It's mostly grunts. It does seem a bit odd that they didn't go with the newest rendition of said koopalings though as it seems they got new voice work for some more recent games, but I don't know if they got different VAs or just new clips. Maybe the new clips just didn't have what they wanted?
Either way, if they own it, they don't really have to get permission. Now, reusing Mario's old clips for Luigi, that may have been pushing the cheap envelope.
Though, I would have liked if they redid Lucina's less than stellar voice work from 4. They even had an excuse with her changing VAs which Ike did too, and they even gave him two sets despite I think him having the same set for Brawl and 4. Though, not everyone is the Star Fox crew which, for better or worse, the fighters seem to have their clips redone every installment. Even if they don't actually get a new VA for some reason. Meanwhile Mario is still using his Brawl clips. Granted, it's Mario.