As far as I know, it's allowed. They can still be targeted from up there and to reach that area in the first place, you just need to jump. Not sure how it would work for a Jedi jumping to them to attack, but I've shot down a few sorc's with my commando that thought they were being slick.
So they aren't really exploiting anything other than being on the high ground in an area that people, normally, don't look at.
Don't see a problem with it, you can still target them and jump to them. Only people with tunnel vision might complain, but than again they would miss the guy on the right or left too.