If I remember correctly, our mohel swabbed some antibiotic and put ointment on it before wrapping it in gauze. No sucking. Like I said, if that had happened, he'd have gotten slugged because no one in our audience would have known about that and would have likely jumped to the same conclusion - that it was inappropriate.
As I see it, this sect is still living a lifestyle that is very much like that of their ancestors in Europe hundreds of years ago. Remember, their ancestors were in ghettos in Europe and lived by the rules of their own, very cloistered community. It is still very cloistered, much like the Amish in Pennsylvania.
Also remember there were no antibiotics until the last century. They also used to bleed people and use leeches as a cure, both absolutely abhorent in the modern world. Some of the ancient "cures" actually did more harm than good, others had their value, the leeches being one example, herbs are another.
It would seem that if this is an old world tradition still practiced, it likely has some value, though clearly it also has substantial risk given any viral or bacterial infection is known to be spread via bodily fluids. Even within a cloistered community, it would seem to me that he had to know he had an active infection, I mean, do you think he'd have done the same if he had the flu? Of course it is possible he had no idea the cold sores constituted a risk. I think this was unfortunately an act of ignorance, not condoned sexual misconduct.