Roos, 27, played seven games with the Seahawks last season. He has appeared in 14 total games.
The Seahawks signed him as an undrafted free agent out of Purdue in 2017.
Las Vegas also waived defensive end Ade Aruna with a non-football injury designation.
Aruna, 26, originally entered the league as a sixth-round choice of the Vikings out of Tulane in 2018. He spent his rookie season on injured reserve.
The Vikings reached an injury settlement with him last season, and he later signed with the Raiders’ practice squad.