If the OSM database is used as is and not used to modify any of their existing data, the existing data wouldn't have to be released. IANAL, but it seems to me that the data could be used in conjunction with existing data for the purposes of rendering tiles and not require releasing any other data sources.

https://opendatacommons.org/licenses/odbl/1.0/

ish. You can generate a map image of it, and combine that with other data and that only requires attribution