Eirik and I cleared this up. Our database setup had gotten slightly mismatched and we were still on derby.
In case others have ended in the same state, we:
1. Ran ambari-server setup to configure the jdbc-driver for mysql
2. Set /etc/hive/conf.server/hive-site.xml to use mysql driver and connection string
3. Set manually /etc/hive/conf.server/hive-site.xml to match the settings from hive-site.xml under conf.server
Then restarting hive sorted the matter.