Can I fly for a part 135 after I've reached 500 hours and still be a part of a cadet program?

Jeff,

I would stay very far away from any 135 carrier if I were you. The reality is that most of these low time jobs are not what they are cracked up to be, They can be dangerous, or not involve much flight time at all. The fastest, most proven track to the airlines is via flight instructing.

Chris