Success is all relative and it depends on what people have been pursuing. Chris has done well with his books, and I think his future is probably more behind the scenes or a character actor rather than as a leading actor. His Hot in Cleveland gig should be fun. He's smart and talented so I think he'll find success in whatever he pursues.
Dianna I think has struggled a lot to find good projects since leaving Glee. Her major studio releases both flopped pretty terribly and they were booked when she was still on Glee. She has some smaller movies in 2014 in post-production. I don't believe they are with any major studios (at least they're not projects I have heard of).
Grant has landed a lead in a CW show, which is pretty good considering he was just a guest star on Glee and hadn't done much before that. That's a great job for him, but you can't compare what a guest star was able to do vs. what a regular cast member was going to do. Lea, Chris, Darren, Chord etc. are obviously not going to go after auditions for network pilots.
The perceived success or non-success of Lea's album is still TBD. Her second video is slated to come out next week so we don't quite now yet how that will all play out. Her book is also coming out next week so that's another thing on the horizon. So in the last year, she's recorded an album, written a book, and landed some pretty high profile endorsement deals and countless magazine covers. That's pretty successful too. Sure she hasn't been in any blockbuster movies, but none of this cast has been and most of them probably never will be.
I think the only absolute right now is the utter failure of Glee this season and probably next. The future success (or not) of the cast members is still TBD.