How will they stay airside if they're doing a turnaround - for instance, surely it's not going to be possible to have their bags tagged through so they'll need to collect them and re-check them in?
There is then the problem of convincing the check-in staff in DXB that you don't need a visa because you're coming straight back again.
Not an issue if you have a connecting flight but they're surely going to be a bit puzzled if your next destination (on a different ticket) is the same as your departure?