I'm not sure about this, but I think that I read/heard somewhere taht JK didnt' want to motto to be something lame like most schools have (I know that my schools were pretty lame) and wanted it to be a funny yet good piece of advice...
after all, it woud be a pretty silly to go up and tickle a sleeping dragon... you might just find yourself burnt to a crisp!!!
And with the connection to Draco... I noticed it a while ago, and spent a bit of time trying to somehow connect them, but couldnt' think of anything, so I reckon that it's just a coincidence!