The dog-like creatures chasing Gregor are called massiffs, first seen in Star Wars: Attack of the Clones. This episode utilizes an updated massiff creature model of the one made for Star Wars: The Clone Wars.
The notion of clone commandos training standard troopers harkens back to the Republic Commando series of novels.
The armor used by the non-clone "TK troopers" takes inspiration from Ralph McQuarrie's original stormtrooper designs created for Star Wars: A New Hope.
Clone Commando Gregor first appeared in the Star Wars: The Clone Wars episode "Missing in Action" and later returned in Star Wars Rebels. Having suffered amnesia and survived a massive explosion, Gregor is a little worse for wear.
Clone commandos were first mentioned in Star Wars: Attack of the Clones, but made popular in the 2005 video game Republic Commando. One of the commandos seen in this episode was designed to resemble RC-1262, a.k.a. Scorch, from that game.
