I don't think so. Keep in mind that he helped Lint behind the scenes well before the events of the manga, and this is the only time we've heard of his wish for revenge.
Whether or not he's evil, there's a phrase we're probably all aware of: The enemy of my enemy is my friend.
I don’t usually use the forums, but i’m going to make an exception since you guys are worrying about a storyline.
In chapter one we saw the spider in a test tube of sorts, implying the girls are genetic experiments. If so, then once the rest of the girls see Washio again, the government/kingdom...