Let's look at the winners:
Tough Enough 1:
Maven - Had a few notable moments, never went past the midcard.
Nidia, valet for Jamie Noble, nothing of note otherwise.
Tough Enough 2:
Jackie Gayda, had one of the worst matches of all time, later a valet for Rico and Charlie Haas.
Linda/Shaniqua, valet for the Bashams, for a short time.
Tough Enough 3:
John Morrison, after forty two name changes, went on to be very successful with a lot of title reigns and feuds. Never managed to get to the main event, but a pretty good career in WWE all the same.
Matt, career derailed by a brain tumor, never wrestled for WWE in the end.
Tough Enough 4:
Daniel Puder, tried to shoot on Kurt Angle, paid for it when Benoit, Eddie and Hardcore Holly ganged up on him in the Royal Rumble to haze the shit out of him. Gone soon after.
Tough Enough 5:
Quiet Anger. Took a stunner, sent back to developmental, released for being shit.
So, uh, one successful career from among the winners.