The Curve Adapters interact with curve pool through three functions, exchange(), remove_liquidity_one_coin() and add_liquidity(). The last parameter of these functions are set to zero, which is the slippage parameter.
Ocean protocol takes care of it by checking the slippage right at the end, but it can also be integrated right into the curve functions.
CurveTricryptoAdapter.sol#L201-L203
