It depends on how they did the tile underneath...if it was done well where the tile goes all the way to underneath the flange with no gaps, then the floor surface should be okay although you may have to do some cleanup if there's any caulk (could leave an outline). If they didn't run the tile everywhere, you might have ugly holes showing.
On the Drake, to get a 10", they use a different tank as I understand it. I'm pretty sure if you swapped tanks, that 12" ADA version tank will fit on the lower one and you'd have the same gap at the rear (iow, it'd be a 12" rough-in toilet). If you just swap the entire toilet with attached tank, then you'll have the gap.