If you don't have flak armor and the wiki's listing of 200 max splash damage for the AH is per pellet (which seems likely), then yes, it can 2-shot you if almost all pellets hit. Of course, the ESF has to get suicidally close to do that.
http://planetside.wikia.com/wiki/M30_Mustang_AH http://planetside.wikia.com/wiki/MAX You can look this site for weapon damage and that kind of thing you can see mustang deal 175x8 damage under 50 meters, max have 2000 health, 2 shot if every pellet hit give you 2800 damage so i guess with the wrong armor, in the 50 meters range you can get two shot.