Can someone use a hyperbaric chamber if he or she has had an aortic aneurysm?

Yes. Hbot is safe in patients with AAA - the AAA should be monitored by a vascular surgeon to determine if it needs to be repaired.
It depends. I assume that the aortic aneurysm has been repaired and the patient is stable; if that is the case, then the this alone is not a reason to preclude the use of the chamber for another approved condition. There are other medical conditions that may have occurred surrounding the aortic aneurysm and its repair that will require a review by the hyperbarist before final approval.