Jesse, Jean shorts would be allowed under rule VI.4 “lower body must be covered by a one piece suit or shorts. The suit or shorts must not extend lower than the base of the quadriceps muscle. An undergarment is allowed to be worn under the suit or shorts, but must not provide any support that would aid in lifting”.
This description appears to allow jean shorts. However, at a National meet they probably would NOT be allowed, as the meet director has authority to disallow any attire which they feel is inappropriate (rule VI.12), which jean shorts possibly could fall under.
So bottom line is this – they are allowed unless the meet director (you) say they are not, but that may not be a wise move on your part as they could result in a fight!! Al