Yep, that's the most common solution, I would go for that.

nick = nickname = username
And yes, of course a bot could use smileys. You know it's not more complicated to write =) than to write "Great".

These bots have a bunch of phrases which they choose...

You know all this reporting of nicks is really useless. If I would've wanted to spam a forum I should've randomized the nicks, and I'm sure these spammers do aswell....