Marshal says Emperor Palpatine has not been in Rebels series. Actually, his voice was heard as a hologram to Darth Vader at the end of the Season 2 opener "The Siege of Lothal": https://www.youtube.com/watch?v=pjigBxuXpww
Marshal mis-quotes the SW:TFA line "Tell that to Kanjiklub." as "Tell it to Kublai Kahn." Kublai Kahn was a Mongol emperor, and also the grandson of Genghis Khan. He has no connection to Star Wars (that we know of).
The character of Saw Gerrera, played by Forest Whitaker in the movie, made his debut in season 5 of The Clone Wars, in the episodes “A War on Two Fronts,” “Front Runners,” “The Soft War,” and “Tipping Points.”