a bit confused

When it says merge network has the same player pool, does that mean that weather you play on sportsbook or carbon you are playing against the same players?

Yes.

The lobby that you'll see on one of the 'skins' (ie. Carbon, Lock, etc.) will be the same on the others. Note: if you're logged in one skin, you won't be able to play on the other at the same time.
(this is the same sorta thing on 'ipoker network', with Titan, myBet, williamhill, etc.)

The only games that would have a different player pool would be private games and sometimes special promos by the individual site.