HiveConnectionPool belongs to the NiFi Hive NAR, which includes a Hive JDBC driver. ConvertJSONToSQL is not in that NAR and thus does not have access to the driver. In this case you would want to download the driver (and any dependencies) into some folder (NOT NiFi's lib/ folder), and add the path to that folder as your value for "Database Driver Location(s)". Then the processor should be able to find the Hive driver.
Having said that, I can't remember offhand if this processor works with a Hive driver or not. If it does, you may still find that you have to use ReplaceText or something to change the generated SQL to proper HiveQL before executing it (presumably with PutHiveQL).