Dogie,
no Bitmain isn't using the p2pool share chain.
Right now:
Pool rate: 3.88PH/s (7.0% DOA+orphan) Share difficulty: 16500000
Third time, you're not listening. Please, actually read what I'm posting this time.
Bitmain's hashing power is on their main NON P2POOL pool for now, there is very little on the p2pool pool as to not upset p2pool.