Any question answered...

would a 30t work on the aforementioned cassette?

That’s going to be a matter of try it and see if it clears the 30. They usually do, but the point Tester was making (let’s say you’ve got 52/42 at the front) is that the derailleur might not be able to accommodate the full range between 52/30 and 42/11. The cage simply might not have enough swing to do it, ie the chain will be too tight at 52/30 and the derailleur will be fully parked backwards at 42/11. You can only really find this out by trying.