Edmondson, 19, made his Leeds debut in the Championship at the age of 16 and spent the first half of this season on loan in Scotland with Aberdeen.
Miller, 25, has made nine Championship appearances for the Millers this term.
"Mickel is a tricky player with pace who can play wide or centrally," boss Keith Curle told the club website.
"He is a goal threat himself and he is also a player who can create opportunities for others.
"Ryan is a mobile, hard working, aggressive centre forward. He has a hunger and a desire to score goals and he is capable of scoring different types of goals. He can link play well and he also has an excellent work ethic."