Is the Aave flashloan work on centralized ex or just dex?

Aave flashloan allows you to draw liquidity of pool for a single tx that is repaid by end of tx. I don't know of any centralized exchanges that lets you do arbitrage like. In most centralized exchanges funds exchange requires multiple block confirmations (in simple terms many more blocks mined) before funds transfers/exchange to the user is completed.

So, short answer I don't think flashloan would work with centralized exchange.