Zhao Hai didn't know what Frost Wolf was doing. If he knew, he would have praised Frost Wolf for his intelligence. The reason why Zhao Hai said that it was useless to let Frost Wolf keep it a secret was because he knew that these people had no intention of keeping it a secret. There was probably a traitor in their gang.
However, Zhao Hai still got Frost Wolf to do some security measures. He only hoped that no one would know about it before the attack at night. Frost Wolf was even better than Zhao Hai. Before the attack at night, he didn't let those people know who they were going to deal with. Although they would be surprised when they attacked, they were already prepared and wouldn't delay things too much. In terms of keeping the secret, it had an unexpected effect.