6/3 UPDATE #2:
The Cubs have signed two second contract minor league free-agents, 1B Francis Reynoso (ex-STL) and RHP Jeral Vizcaino (ex-MIL), and they will play in the DSL (Reynoso was assigned to DSL Cubs Blue, and Vizcaino was assigned to DSL Cubs Red).
Normally a player cannot play in the DSL once he has played in a U. S. minor league (Reynoso played for the FCL Cardinals last season), but that restriction does not apply to second contract players.
A "second contract player" is a player who does not yet qualify to be a MLB Rule 9 minor league 6YFA but who has been previously released or non-tendered in his career (even if the player re-signs with the same team after being released or non-tendered, and even if he has been released or non-tendered more than once).