Yes, being Diamond will get you a room upgrade, lounge access and free breakfast (lounge or restaurant) at the Hilton. They will give you a little card showing all your benefits and timings of lounge and so on when you check in.
Best/shortest way to get from Hilton to T2 is across the walkway towards T1 then left down the escalators (one flight) to the bus that will transfer you to check-in level at T2.