[quote=BKburke]
A spy. Ok. But I'm not sure about his history. I don't know how then people under the empire are treated and such. And if they are as organized as I believe then I'm sure they would want certain races as certain roles.
[/quote]

They are the EVIIIIIL EMPIRE! What do you think about how they are treated?
Well if they fulfill their purpose, and obey the laws. Merciless to those who are not useful to the State.
For a 'Spy Caste', they would want educated individuals, and ones who are naturally mobile, in order to best get to the destination and fulfill the purpose. 
So Gnomes, Halflings, and Elves would be the members of the Spy Caste, due to natural advantages in mobility and they are all civilized individuals. And of course Humans, because Humans are the most common race and blend in most everywhere.