Minting with yCRV or yUSD doesn't incur a fee and doesn't cause slippage. We use the curve pricing function to give an exact amount of DUSD.
While minting with stablecoins (Dai/Tether/USDC/TUSD), since these are deposited to curve, a 0.04% fee is charged. This is reflected in the amount of DUSD that the user receives. The DefiDollar protocol doesn't charge a separate fee.