As the title suggests, yes, I've seen an Imperial Centurion during the quest for the Imperials at Fort Dunstad. He was part of the fighting group, and carried also the rare horseman helmet.
I don't know, if this is just because I have some mods on my PS4 on, but I was during the quest/am lvl 94 in Skyrim, and would suggest that this character appears at specific level. What the level is, I have no idea, but I definitely will look into it... AND hope someone else will to!
Best of regards from Finland
TJ
FOR THE EMPEROR!