My question would be, why would you need to add the root user to these groups? root has access to everything no matter, so adding them to these groups unless its required by a service on the server or host, I don't see the point.
Though adding users to these groups would make more sense, to those who would need access to files and directories owned by the groups in question..
But to add users to these groups manually, you'd simply add them to each group.. like this:
Code:
piranha:x:60:
netdump:x:34:
oinstall:x:500:root
dba:x:501:oracle,root
oper:x:502: