At the moment, if you activate "hibernate.hbm2ddl.auto=validate", then hbm2ddl will fail since it won't look for synonyms.
The related code seems to be in DatabaseMetadata :
might be replaced with something like
I'm gonna have a look at the code to see if I can provide a patch.
I also found some seemingly related JIRAs, but I filed this one since I didn't find something specific to synonyms (I'll also have to get my hands dirty with Gradle, fingers crossed ).