Desmond clinched two state championships at Bethlehem Catholic as a freshman and sophomore.
Nickal is 5-0 in UFC duals and most recently recorded a knockout victory over Val Woodburn in July.
Allen was previously a graduate assistant in Bloomington before his father's firing.
Herron verbally committed to Penn State on December 11.
"The bottom line is that it was a great game and that was a great week for the Indiana Hoosiers."
Probst, listed as an offensive lineman, defensive end, and linebacker, will join the Nittany Lions' recruiting Class of 2024 as a preferred walk-on.