Yes, but you have to read the next book "The Ghost Brigades" and you'll get a little more information on what they look like, but not a lot.
For some reason, I remember imagining that the Rraey look like humanoid birds or chickens because they squawk a lot during battle.
On page 15 of the Ghost Brigades: a Rraey is examining humans.
And he describes the human (he also describes himself) as roughly the same size and shape as he is, bipedal, and bilaterally symmetrical.
The Rraey also notes the differences: However, human knees bend the opposite way and the human torso is broader as is the abdominal plain with a generally awkward skeletal structure and musculature.
He also notes that humans have club like hands and stump like feet. (So he must have the opposite)
He also notes that humans have only 2 eyes and ears whereas he has eyes and ears that wrap all the way around his head. And he has heat radiating folds of skin on his head instead of hair. (I imagined that this is like a roosters comb for some reason, I don't know if this interpretation is correct)
That's all I could find/remember, there might be more hints but I would have to read the book again.