From the appearance and location (and lack of other typical symptoms), I would not
suspect that it is a case of sarcoptic mange. I'd also be a bit sceptical about demodecic mange - but much less definitively so (i.e. I think it is still worth asking your vet to take a skin scraping for that one).
Since it doesn't itch though, I wouldn't immediately assume that the cause is any sort of allergy (it's possible, but not classical). My general thoughts would tend toward either bug bites, or some dermatological problem. Little scabs like that could also airse from small scrapes/scrathes - I know it's winter and you're in a cold part of the world, but does he spend much time outdoors in the yard? What I'm wondering about is whether there's a possibility of little scrapes occuring from him rooting about in shrubs, etc.