Yes, you can host a fmp12 file on FMP14. The file format for fmp12-fmp14 is fmp12. FMP14 has features that were not available in FMP12, so if the database is created in FMP14 then a user connecting with FMP12 will not be able to run any part of the database that has the new feature. For Example Popovers were added in FMP13, so a FMP12 client will not be able to use popovers.
Thank you - I assumed as much, but was looking for additional conformation.