yeah, all rare monsters can be seen on all difficulties and their appearance rate is the same, and they do drop rares, most of the time, materials.
meh...that's like saying lv30 tech disks are rare, they are in theory but they don't actually come in red boxes (which is what the game considers to be a rare). I agree with you that mats and lv30 tech disks are rare but they aren't classified as rare. So, yes on normal mode you can see anything (that's why the pop up in cmode from time to time :O ) but you can't get rares from them.