I like the start. I can't speak to the accuracy of the Vong details because I haven't read the Vong books.
I would add a little more scene description to add color so I can 'see' what's going on. When you can, let the characters talk to each other to give the story instead of you as narrator telling me. If someone is nervous, instead of telling me 'he's nervous', describe what he's doing that shows he's nervous--is he fidgeting? Tapping his foot? That kind of thing. The conversation between Ralik and Xerx was interesting. The only thing that caught my eye was Ralik questioning Xerx openly--in those kinds of society, you could get struck down dead for questioning orders like that.
However, that's a little detail.