It was definitely Ted Knight as Winston. Shatner didn't play any characters in TAS other than Kirk (or in this case, the Vendorian impersonating Kirk). Knight did a lot of voices for Filmation, including most of the supporting cast in the '68 Batman
cartoon and the lead roles in Fantastic Voyage
and Lassie's Rescue Rangers
, as well as serving as the announcer on those shows and Hanna-Barbera's Super Friends
. And it never occurred to me that anyone could mistake his voice for Shatner's. Shatner's voice wasn't that deep in the '70s.