id presume you just have to keep an eye on them much like you would your own. keep a note on where they are, and look for any changes in things like size, colour, shape etc..

i'd say if your dh gets heaps of them, if they are harmless ones it should be fine. but obviously if he has had to have some removed, or not harmless maybe get your son into a skincare clinic, so they can show you what to look for and have regular checkups. (infact, make a family day of it and get everyone regularly checked up)