That's correct. We (I work at Looker) are written to leverage the analytical capabilities of SQL. So we support all kinds of SQL implementations, from totally standard (PG, MySQL, MS) to MPPs (Redshift, BigQuery) to SQL-on-Hadoop (Hive, Impala, Presto, Spark).

But the JDBC -> Druid connectors that exist look pretty janky. So if someone builds a stable connector, I suspect we'd support it. But for the moment, no Druid.