Is the expiation for an oath (kaffarat al-yamin) valid if the one who paid it intended it as expiation, but the agent who delivered it did not intend or know that it was expiation, and therefore did not inform those who received it?

It is not permissible to pay the monetary value of food or clothing for an expiation of an oath according to the majority of scholars. However, it suffices if it is done with the intention of expiation, following the madhhab of Abu Hanifa. It is not necessary to inform the indigent person of the true nature of the expiation, just as it is not necessary to inform the recipient of zakat that it is zakat. If you deputize someone to pay the expiation, your intention is sufficient, and the agent's intention is not required, though it is preferable to inform the agent of the intention when paying the beneficiaries. Expiation, like zakat, requires intention.