This man, I read, was a former Army Ranger. It is not completely out of the realm of possibility that he could have easily been an intelligence asset on the ground. Aide worker is a good cover for such doings.
Regarding the man’s conversion to Islam.... My understanding is that if you are captured by these monsters that beheading can be the least painful way out of their captivity. I’ve noticed that the two who already had their heads removed appeared to almost welcome it or were resigned to get things over with. If a conversion lets one “skip the pleasantries” of IS torture before your beheading, then I can hardly blame some for doing it. Hopefully, few will ever have to walk in those shoes. Let God do the judging after the fact.
Lastly, the man was an American and a former Ranger. Condolences to his loved ones and RIP to him.