Yes, as a Club cardholder, you can enter the United Club with one guest, and use an Explorer card one-time pass for a second guest.

As a lifetime United Club member, I have often left and returned to the Club. On more than one occasion, I have brought in a guest on a subsequent entry -- once for an acquaintance seated near the very back of a plane where I was seated near the front and wanted to rush off to clear immigration and customs.