Nien Nunb might be in Rogue One.
He is Lando’s alien co-pilot in Return of the Jedi.
It seems unlikely that well see any Sullustans in RO as they canonically (in both btw) only joined the Rebel Alliance shortly before the Battle of Endor.
That wouldn’t have much affect on when individual members of the species joined the Rebellion. For example, in the Legends canon it was a Sullustan that scouted out Yavin IV before it became the home of the hidden Rebel base.
That aside, the thing that discredits the idea that Nien Nunb is in Rogue One is the fact that at that time he was still a smuggler in the current canon. Which was revealed in a Marvel comic back in June of last year.