Dogie,

no Bitmain isn't using the p2pool share chain.

Right now:
Pool rate: 3.88PH/s (7.0% DOA+orphan) Share difficulty: 16500000

murraypaul:

if they were using the p2pool sharechain, they can't divide their payment up into 2 addresses in the coinbase payout.
They can pay it to themselves, as the p2pool does, and then later distribute it based on some fee/nofee calculation of course - but that of course won't be all the tx fees, just their payout % of them.
But as I said at the start of this post, they aren't using the p2pool share chain anyway.