Let me just share our recent experience of hire car from Bergamo Airport in the case that i might help anyone else with their trip. Clearly at the time we went ( June 2014) there was still development work going on, so things may change in the future. But right now, the situation we found was:
a) the signs to car hire from the departure area after customs are WRONG. They point you outside - but the car hire desks are actually inside the terminal ( turn right after leaving departures).
b) there is a bus to the car hire area that is shared by all the car hire firms. It waits to fill up at the remote parking area - so may not be that frequent ( we waited 20 minutes). Don't leave it too tight when coming back !
c) the biggest problem is that the car hire return area is not signed from the airport approach road. There was a sign near the terminal - but it was wrong. In fact the area is well before the terminal, a turning almost immediately to the left once you get onto the airport approach road. My advice is take a good look round when picking up the hire car - it will help bringing it back. It I had been really organised, I would have got my sat nav to have stored the starting position before we left.
It may be a temporary arrangement - so everything might be fine when you get there. But if not, I hope I've helped just a little. Have a good trip!