The feed-in credits don't typically get paid out - they're added to your account with the supplier. Some PV customers could have a healthy credit balances build up in the summer from FIT and then use that up in the winter months. However you can request a refund of your outstanding balance with your existing supplier when you move (as would be the the best thing to do in many cases when new customer rates/discounts expire after 12 months). If you're not moving and want the balance paid out, I would say a refund is possible. There is no relationship between your FIT credits and other utility bills.
Note: it will ultimately be possible to receive FIT credits from suppliers other than your own electricity supplier (i.e. you sell your credits to SSE, have your electricity supplied by Bord Gais Energy).