Although it was a fair time ago, my experience of the UAS recruitment process was that we were always very much oversubscribed, so any filter that reduced the number of potential interviews was strictly applied, hence the initial medical questionaire, where a 'YES' responce automatically ruled you out of further consideration.
We also had a number of people who followed up this rejection with a letter to the CO, and in many cases this resulted in an interview and subsequent selection.
However, the bottom line is that no one has a right to be granted a place on a UAS, and in the end, it is the decision of the staff and CO that determines who joins.