Is it allowed and possible to make “bulk” use of the entire (or regional) OpenStreetMap database for commercial purposes?
If by database you mean using the data by downloading the data ( http://wiki.openstreetmap.org/wiki/Planet ) and using it in your own applications then yes as long as you comply with CC-BY-SA licenses, which does allow using the data for any purpose including commercial and in any quantity.
However if by database, you mean the actual OSM database servers in the form of API requests, the answer is probably no, as the the servers have rather limited capacity and can only just sustain the load coming from users editing the data, but definitely not commercial users querying the api for their apps. ( http://wiki.openstreetmap.org/wiki/Acceptable_Use_Policy ). But then, you can just do the above and set up your own server with a full copy of the data