So...yeah. About archetypes.
Actually, looking at Hitchhiker's is a good example of how aliens aren't all the same. There are a vast amount of races explored in Hitchhikers, and they all act vastly different. Then again, they aren't necessarily confronted with life on Earth.
Take Star Trek, though. Aliens and humans intermix frequently, and rarely do you run into an 'Ax' character.
In short, I think that there are alien archetypeS, emphasis on the 's'. There is not one way for aliens to act. There is the 'emotionally reserved' alien, the 'humanity-obsessed' alien, the 'violent-culture alien' and so on and so forth.