If my short term memory serves me right, his debut was a crap game against Benfica, where he was murdered. In his defence, think he played left back, which is not simply the same as playing right back.
It could be that Moyes doesn't trust him as yet, but again if memory serves me right he was played out of position, and when he has played in his proper position he's made a telling contribution.
With Hibbert's hamstring (hopefully) keeping hm out for a few games, it would really be a crime not to play him. You don't buy a 21 year old to put in the rezzies, so I trust that Moyes does see a future for him.
BTW I'm not a Hibbert hater, but competition in any position should be the norm to keep everyone on their toes to ensure they perform at the highest level all the time.