Terms of the deals were not disclosed.
Oystrick has played 65 career NHL games with three teams after being a seventh-round draft pick by Atlanta in 2002. He had a goal and two assists with St. Louis last season.
Arsene spent last season with Peoria of the AHL and played 13 games with Edmonton in 2009-10 without registering a point.
A fifth-round pick by Dallas in 2005, Watkins played for San Antonio of the AHL last season, scoring 15 goals.