Strictly speaking, this is not an arbitrage, because (a) you run the risk of not getting an above-inflation pay rise, and (b) even if such a pay rise is a certainty, you are locking your money up while you wait for it. The latter point makes it a carry trade, rather than an arbitrage.

If you could sell your future interest in refundable vacation days now, for more than it cost you to buy them, that would be an arbitrage.