A bad grappler is someone who leaves himself vulnerable or unsecure because he hasn't been taught another way.
An unorthodox grappler is someone who intentionally does something different to common convention even if he knows the risks.
Unconventional grappling is becoming easier to define now, because with MMA/sub grappling giving most grappling styles a focus point so many grapplers are starting to fight the same to win matches, even if their styles are different. Judoka and Catch wrestlers both respect full mount, acknowledge the danger of full guard, and know rolling to your stomach can get you in trouble.
Before rolling to your stomach was seen as standard in some grappling styles. Even trained wrestlers who compete in submission wrestling know it is a dangerous move so they don't do it.
A wrestler who knows the danger of giving up his back and consistantly does it as part of his strategy would be an unorthodox grappler.
Attempting a Kimura while in your opponents guard while knowing it is low percentage would be unorthodox.
My teacher turns around when he is in his opponents guard and works to break his opponents feet while backmounted. The second the opponent opens his legs, he passes. Very dangerous move, but he always pulls it off. It is unorthodox now.
Keep in mind, once a new strategy becomes common it will no longer be unorthodox. 5 years ago the rubber guard was unorthodox. I predict in 10 years it wont be.