Can diseases affect NPCs and creatures in Skyrim?
While I cannot give you definitive evidence with a picture or such, I can tell you that I've seen enemy's show the contracted disease effect before after taking damage from a wolf's attack, whether or not it actually applied any debuff's is unknown, but it's highly likely.
Yes It does. I went to a imperial camp in the Reach trying to talk to Legate Rikkie but then a bear attacked an imperial solider then in one of his attack he got light for a second (I think he has rockjoint). I went back to a save and it always does that so I think that they can get the disease.