I've seen tanks drilled a few times, why don't you buy a bit and try yourself? A glass shop used a small portable drill press and slapped a hole in a 10 gallon tank within seconds. the 1/4" glass on a bigger tank took a little while longer by another aquarium shop using a regular free-hand drill. diamond coated hole saw bit
The ato reservoir is so small. I don't think it's worth it. To each their own, but if you have the space, why not go with a baffle like reefdreams created? If customking (Jeff) can make it, that would be a better option IMO.
Your tank, your choice.
I have the RSR350 and switching that over to a custom lid for that compartment. place a skimmate holder in it's place and a latch door to access my filter cups. the ATO is bulky and takes up space + an eyesore.