Had they lasted long enough, Willard probably would have been thrown under the "grunge" moniker. I say that based only on the fact that they were a hard rock/metal band from Seattle. Of course there are examples of bands that prove that theory correct, such as Alice in Chains and Soundgarden. This was fairly common at the time. But Willard did not last long. Their only full-length was released in July of 1992, a full two months before Nirvana released Nevermind. They broke up some time afterwards. So no, they are not often named as part of the grunge scene, but likely would have been.
Instead, Willard played a style of stoner/doom metal and were very similar in style to the more metallic moments of fellow Seattle band the Melvins. Their music is fairly simple and direct: distorted Sabbath-style riffs, throbbing bass, and punk-esque vocals.
These guys suffered from bad timing, releasing their only album two months before Nirvana. Therefore they faded into obscurity. Who knows what would have happened had they stuck around?