That's why I decided to try the striker role for monsters. The artsy rogue would make a decent skirmisher, but the cool rogues don't really fit any of the monster roles. (No, I'm not biased at all.

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Alright.
I guess I'm saying they seem a little "boring". They just have combat advantage going for them. They'll ambush with their Stealth skill, but then every round, they will (slowly) try to flank enemies to get combat advantage. That's all they do. IMO, they need something to be more interesting.
One thing you could try is making Tactical Strike a trait, like this:
Tactical Strike (martial): The rogue has combat advantage against any enemy that is adjacent to at least one of the rogue's allies.
As I like doing, it's a simpler version of a PC power. (The E-thief has the same ability as an at-will move action, which also prevents the rogue from provoking opportunity attacks if it moves from a square adjacent to an ally.)
The dwarves now work better as a team. They don't need to try to tumble around and flank, it's just that any PC facing two of them will be in a world of pain. The defenders and controllers will have to work extra hard to guard vulnerable PCs and split up the attackers.
(I believe this trait would also make shuriken nasty. If a rogue is next to a PC, a rogue 10 squares away can still hit that PC with their shuriken, gaining +2 to hit and +2d6 damage.)
Striker aside though, I could probably tweak brute stats to make it work for rogue npcs.
The funny thing is, that would work, but IMO that's not flavorful. (Brutes work well with Slayers, who don't have to work as hard for extra damage, but don't get the benefits of combat advantage whenever they feel like.)