Is it permissible to count the amount paid as a loan from our Zakat, with the intention of informing him later that it is a gift?

You are not permitted to pay Zakat except to someone whom you predominantly believe to be poor and deserving of Zakat. If your wife informs you that they are not deserving, then it is not permissible to pay Zakat to them, and this payment will not be sufficient for you. It is permissible to pay Zakat to someone whose entitlement you are certain of or predominantly believe, as well as to someone intending to marry who is unable to afford the conventional expenses. The majority of scholars do not stipulate informing the recipient that it is Zakat, unless they would not accept it otherwise.