Well, it isn't a bad thing, it shows he is accepting her, as he accepted your previous dog. ;-)
I truthfully don't understand why some male dogs do this, a pup usually licks the mouth of an adult for food, and in a pack the lesser dogs will always lick the mouth/face of an Alpha dog/bitch to show they accept them as the Alpha. But why some male dogs will sodden a pup or guinea-pig :-D I don't understand.
My mum's terrier x will lick and lick something to weaken it, so that she can then rip it open (hence a cushion) but it is not for that reason don't worry.

I can't understand the benefit of doing it or what it means, apart from acceptance. Glad they are all getting along well, he sounds to be a good father figure.