The only solution I was able to find is to completely give up on providing instance names for either the zero-thread or multi-thred schedulers.
This results in all scheduler names defaulting to QuartzScheduler
and that makes all the jobs/trigger created by any scheduler visible to the zero-thread scheduler used by my UI to display and manage jobs/triggers...
I also tested my hot folders by droping multiple files at once into the hot folder which resulted in instantiation of multiple custom FileProcessor
objects with each one using its own zero-thread scheduler and no exceptions were raised by Quartz due to all these simultaneously created zero-thread schedulers using the same default name.
I would prefer to be able to continue using different instance names for different schedulers but this resolved the problem so it's an acceptable solution.