No, not really—
The AT-AT walkers have very thick armor, high-caliber weaponry and an infinite range advantage. The only possible way that TWD could beat AT-AT’s is if they’re outnumbered by, like, 10,000+ to one, but that’s not possible.
Why, you may ask?
Well, in Star Wars, AT-AT’s are NEVER deployed alone—always in groups of at least five. Also, even though there are literal BILLIONS of zombies, there’s no way that even much more than a few million could come at them at once; it’s just not possible because of how much land they would need. Also, AT-AT’s would likely have support, such as Twin-Ion Engine fighters, bombers, and Venator-Class starships.
The zombies wouldn’t stand a chance.