I would go to a pharmacy and ask if they can give you the same/similar type of dressing to replace the neck one, otherwise reinforce the edge of it with the tape - doesn't matter if it's not 100% waterproof so long as he keeps it dry.

If there's a sutured down dressing on the ear that will keep the graft covered and clean. The outer layers sound like they're mostly cosmetic if you know what I mean. The sutured down dressings on the grafts can look very crusty and ugly.

Of course if you're really worried there's never any harm in getting it checked.