I never had the heart to tell him that he was just dribbling...
Yeah, best never to mention it! Just smile widely and go, "Oooh, you're SO good at that!" [provided they haven't actually bitten you or otherwise caused injury].
The awkward bit comes when they're ready to have sex after RO so you apply condom + lube and they look a bit puzzled but, honestly - their saliva is NOT a good lubricant; it goes dry really fast, which is really bad for the condom, and also it's a bit icky because MOUTH BACTERIA.
Mouth bacteria haunts my nightmares.