I think if you arrive in HAM from a non-Schengen area (e.g. UK) and are on a remote postion thus having to use the bus, you will not be able to go to the departures area. You will have to go through immigration and will not be able to re-enter until you have a connecting boarding pass and go through security again.

At least I could not find a way of bypassing the immigration without setting off several alarm systems...