Those are multipools, simply mining the most profitable coin at that particular moment (depends on the algo), convert it to BTC and buys DASH for you if you want to be paid out in DASH. The diffuculty only relates to X11 mining. Multipools will only help the price as it will directly buy from sell side.
Okay, got it. So i guess its GPU farms that drive the difficulty up then at certain moments for Dash...