I have CC accounts with several UK betting sites, whenever I withdraw in sterling I get the current ex rate. Its considered a merchant refund no different to getting money back on faulty goods so I guess youd have to pick up ex rate as theyre giving you back the same amount as you gave them, currency notwithstanding.
Quick aside, anyone else know that CC companies (at least AIB) dont see this as a payment. e.g. CC bal = 500 euro, 300 of is to paddy power. withdraw 400 back to CC so bal = 100, CC company will say you havent made any payments, youve just got a merchant refund and they'll still charge you interest on the 500 (happened to me). To pursue this with them I withdrew over the balance from PPs so I was in credit with them and I asked them did I still owe them money, noone (had manager on phone) was able to give me an answer but were admant that as long I was i had a DR bal I owed them the full amount.