on a kerberized cluster should the admin rights be granted to the 'impala' and 'hive' service users in order to access hbase tables via those services ?
For Impala I don't know. but for Hive yes, that was the case when I last tested.
You need to give proper permission to "hive" user in HBase.
Since all access done from Hive to HBase (Hive table using the HBase Storage Handler) will be handled by the "hive" user.
You can handle "end-user" permissions on Hive-side for this use case.