<Snipped quote by Mardox>
Assuming they meet on land and not in space? Probably by vanishing via their camouflaging technology and trying to evade them before reevaluating their approach with these creatures.
If the Namilee were able to get the "jump," so to speak, they'd probably appear out of nowhere and make their presence known before trying to demonstrate through gesture they have no harmful intentions. They'd probably try to react in a reciprocal manner to the aliens, assuming the aliens weren't displaying clearly hostile behavior. Again: hostile behavior would probably prompt their retreat.
And what if someone stared at them like they were a piece of merchandise, clearly sizing up all their weaknesses and strengths as one would with a horse? Then asked for a gene sample and to see sketches of their entire biological systems?
Because that's how Xim greet everyone. Until you prove your intelligence, you aren't a person so much as just a wad of raw organic material, which should be refined and modified into a more perfect form.
The Xim have a lot of strengths- they're smarter, stronger, healthier, hardier, and faster than most others- but diplomacy is not one of them.