If you want the healthy fauna of his 'live' rock, then don't dip it... Live rock is just that, alive with countless micro fauna, dipping it could cause die-off and then huge ammonia/etc leaching
You could sorta-quarantine it if you had another tank that didn't have any fish/rock/etc/etc in it (say a dedicated tank for water changes/etc) -- but you'd really only be quarantining for the larger-critters (evil crabs, mantis shrimp, etc), the micro fauna will find it's way into the water column no matter where the rock is put.
I have on 2 occasions taken live rock from tanks that I trusted to not have really bad things in it -- but it's still a risk.