I had a stay at the Sheraton Roma West hotel in Oct. Although this property is a bit further out than the one you are looking at, it just may have a more frequent bus service (about 15 people) to the city, airport and station.
During my 2 day stay, I never once felt inconvenienced due to infrequency of schedules. The thing to remember though is that the hotel seems to host many intl budget travellers and the last two buses from Rome to the hotel can get full. I saw an IDB
once. The hotel of course offers no comp in these cases as the shuttle service is comp anyway and no assurances of its performance are made.