I've seen the plans for the rack youre talking about before, but I havent seen the new tubs with the hole.
Anyway, I breed rats, and I'm telling you straight from my experience- of there's an edge to chew on, it will get chewed on. If theres a hole, they'll make it bigger. I'd patch it with whatever you can the best you can and keep an eye on it. If it starts to get bigger dont tell yourself that theyre gonna stop chewing on it, make sure they stop chewing on it. I had a rat chew through a critter cage wire top one time and I can tell you that it wasnt fun searching for 7-10 rats at 2am in the cold... lol.

But if what BeardedDragon said is right, ...if it's built right and they cant get to it, then dont worry about it.