As far as I know flexicrew don't get paid leave, end of, period. You can take unpaid leave however it isn't available during the summer months when it's all hands on deck. This is because you're working as a contractor - so essentially are self employed.
I'm not sure I buy into this huge queue of experienced FOs waiting to join seeing as many many 3 stripers are leaving for BA, etc. I guess there's the people who can't apply to BA but there are still very attractive jobs in other places.