alleto is a highly regarded center, though it seems that no center is going to get much in the way of stars. look at the scout 300 center listing:
http://recruiting.scout.com/a.z?s=73&p=9&c=4&pid=9&yr=2009
there are only 4 rated centers. 1 4-star, 3 3 stars. alleto is listed at 5, though who knows what they means since he is nr (not rated). it surprises me that centers don't carry the weight of other o-line positions. you always hear that they are the "qb" of the line, and make the blocking calls.
regarding the number of offers versus the available spots, it is hard to tell how many offers byu can make, since more and more are graduating hs and leaving on missions. iirc in the -08 class 5 will be leaving on missions so they won't count until the -10 class. i'm just glad i don't have to keep track of it.
this much i do know, the -09 class is stocked with top shelf lds athletes, and byu is sitting on a short-stack of schollies. that's unfortunate.