Orc Skirmisher has forced effect: "After Orc Skirmisher engages a player, that player must either deal 3 damage to a character he controls, or remove 1 time counter from the current quest."

Can I deal these 3 damage to a character that has only 2 hit points?

I see no reason why not.

Yes, you can do that.

Otherwise you could optionally engage some Hummerhorns and they will do nothing in your Hobbit deck.