Allen's past jobs have taken him through Indiana, USF, Ole Miss, and several other college and high school programs.
Probst, listed as an offensive lineman, defensive end, and linebacker, will join the Nittany Lions' recruiting Class of 2024 as a preferred walk-on.
Allen was previously the head coach at Indiana.
Though it was mostly a slow week for the once-Penn Staters, the Nittany Lions leaguers hit the turf and punched numbers into the stat books.
Parker was Penn State's wide receivers coach in 2019.
Meyer has two seasons of eligibility remaining.