Wookiepedia aborda isso detalhadamente na seção " Uso imperial " do artigo AT-TE
During the Galactic Civil War, surviving AT-TEs were still used by the Empire, mainly in campaigns in the Outer Rim Territories.(Source: *The New Essential Guide to Vehicles and Vessels)
The walkers no longer held a primary status in military campaigns, but were sometimes used for additional fire-support alongside larger assault vehicles, including AT-AT walkers and Juggernaut tanks. (source: Star Wars: Rebellion: My Brother, My Enemy)