Well, nevermind :-) By digging through code, I discovered that by adding ;showSchema=true to the end of the URL enable the API to return something.
Would it be possible to implement UcanaccessDatabaseMetadata.getCatalogs() sor that it returns <something> (really anything beside unsupported). Since it is unsupported, utilities that extract catalog info (for version control, diffing, export, etc.) break since they often make a call to getCatalogs().</something>