We’re in the same boat with our dependent care FSA

What I do is consider the expense as a monthly bill (since our daycare costs are more than we allowed by law to put into an FSA anyway), then I have the reimbursement as a line of income. My husband gets paid biweekly, so we have to budget based on when checks come in anyway (rather than just monthly), so that’s just considered another line that we have to budget based on timing. I’ll often try to have the daycare check writing co-incide with that reimbursement, but it doesn’t always happen that way. We usually get our “invoice” from the previous month the first week of the following month (but must be paid current at all times, so it’s not just like a bill to pay) and I receive my FSA reimbursement pretty quickly, so it’s put into the spreadsheet to be anticipated around mid-month. I know many people that don’t request reimbursement monthly, but we don’t really have room in our budget to upfront the money for months (or a year) at a time.
It’s a pain because it’s a reimbursement, so you basically always have to budget it a month ahead — but it works for us!

I always put one of our two OOP maximum amounts in our FSA

This way, I know that at least 50% of our potential total hospital/doctor visit expenditures are covered for the year and we save a little on the taxes. The rest, we just cash flow.
Between prescriptions and co-payments, I know it will all get used by the end of the year with no problem. This year and last, we blew through it in the first two weeks of January (darn dialysis!)
Now that by the grace of God, I have received a kidney transplant, I think it will take us a lot longer to go through the FSA money during the course of the next year, especially since I will be covered by Medicare primary starting in October until April of 2016.
To answer your specific question, I do not treat FSA reimbursements as part of the debt snowball. If I have extra cash and pay the medical bill without needing to replace that money in another budget category, then I might put it in the snowball as an extra payment.