es, he was. He is listed in the SS-Dienstalterslisten as being with the SD-Hauptamt (DAL of 1 July 1935, 1 Dec. 1936, 1 Dec. 1938 and 1 Dec. 1937) and later with the Reichssicherheitshauptamt (DAL of 30 Jan. 1944 and 9 Nov. 1944).
By the way, Wendler's sister Hilde was married to Heinrich Himmler's older brother Gebhard. Wendler got along very well with Heinrich, too.