I believe that silent slay does pretty much the same thing as slay: Kills the player wherever they're at, then the player can click to respawn. The only difference with silent slay is that it doesn't leave a ragdoll, or make any sounds at all, they just kinda vanish.
So in other words, yeah, it does (in a sense) send them back to a spawn point as soon as they respawn, but, if a player is already dead, then it essentially has no effect, so ULX says:
*DEAD* [ULX]Stickly Man!: !sslay sti
[ULX]Stickly Man! is already dead!