Doesn't look like you got any reply yet. This is something that I am currently researching but I tend to believe they are illegal in WA. I have sent an email off to the State Patrol but have yet to hear back from them. Here is what the RCW states about bumpers:
Bumpers, unless specifically exempted above, must:
(a) Be at least four and one-half inches in vertical height.
(b) Be centered on the vehicle's centerline.
(c) Extend no less than the width of the respective wheel track distances.
(d) Be attached to the vehicle in a manner equivalent to the original manufacturer's installation.
(e) Be horizontal load bearing and attach to the vehicle frame to effectively transfer energy when impacted.
I am guessing (C) makes the stubby illegal. I have talked to a local 4WD shop and they said that they believe it isn't up to the code in the RCW but that only an officer looking for an excuse would pull you over for it. He also explained that most people are out of compliance with stock vehicles from the factory. I have my feelers out on other forums trying to see how many of the people in WA have been pulled over for the stubby. I will let you know if I get anymore information.