I get it; you use a pressure washer to quickly clean your car, so why not your grill? Well, in the case of a pellet grill, I wouldn't encourage you to do so for a couple of reasons.

First off, a pellet grill/smoker has a lot of electrical components (Controller, Auger Motor, Fan etc). While pellet grills/smokers are designed to be weather/rain resistant, a pressure washer is a very different beast that will get water into all sorts of places and potentially damage these electric components.

Second, you don't want to get any water inside the hopper, especially if there are pellets in there. Even if the pellet hopper was empty, you would need to be absolutely certain inside the hopper was dry before loading any pellets, or you're just going to give yourself a headache sorting out the aftermath.