If given the chance there would be a lot of coaches that could be successful in the NBL.
You will find that most SEABL and state league coaches are putting 20+ hours a week into their teams, plus holding down a regular job.
Given the opportunity to become a professional coach I believe you would find that many of these guys would be successful.
Where do you think a Beveridge, Dennis, Gleeson etc started? They didn't just become NBL coaches overnight. Most of them would have graduated up through juniors, nationals, seniors etc...
Very similar with players, there would be a lot of players in SEABL and state leagues that could be handy NBL players if given an opportunity...
Teys from Adelaide is a classic example. A state league player, then development/role player and now a major part of the rotation...