Martinez adds to the Terps' guard depth, while Hamilton was squeezed out of the rotation.
Smart played in 22 games as a freshman, tallying 30 points.
Russell averaged 14.7 points, 4.5 rebounds and 4.5 assists with Rhode Island this season.
Wahab fills a desperate need for the Terps in the low post.
Campbell led the Terps with 10.5 sacks per game in 2020.
The Terps also secured wide receiver Marcus Fleming as a transfer from Nebraska.
He entered the transfer portal Aug. 21.
Tagovailoa transferred from Alabama in May.
The quarterback had announced his intent to leave the program in early February.
In a statement, Tomaic said he was open to returning to the Terps.