If I recall correctly aren't there rules for combining individual CRs to determine the CR of an encounter? If so, I would have to say that killing ~100 1st or 2nd level hobgoblin warriors is probably at least close to if not within CR 7-12 - in which case he should get some xp. Granted, many DMs just say that if the individuals are not high enough to grant at least a little xp on their own then even if slaying several thousand in one encounter you get no xp. I'm not one of them, but I have met a few DMs like that.