Why, yes it is. From the FAQ at warhammervault.ign.com:
[quote]
"Games Workshop would never allow for High Elf or Dwarf to have stealth units since it’s not in the nature of their armies to hide. The Empire would be the next possible option, but again it falls in that theme of army, they may not try to hide while fighting the force of Chaos. While it possible that The Empire may have them it does go against conventional Games Workshop intellectual property.
"Again, this game while it has been developed by Mythic, they have to pass all of the character design and world design through GW, and should GW find not to be in the theme of their game they will say no."
[/quote]