As is often the case, banking procedures are telegenic but do not match reality. A person does not need to travel to the country of the bank in order to withdraw funds (unless an in-person meeting is required for the bank's own policy, but nearly every bank will accept a faxed signed letter of authorization). An accountant could not withdraw funds from a bank account unless he has been authorized by the account owner. $70 million should not need to be withdrawn in cash (the reason for doing it in person), as that would be excessively bulky in any extant US dollar denomination. There is no such thing as a "withdrawal log," although records are usually kept of wire recipients. Finally, money cannot be withdrawn as bearer bonds; bearer bonds are issued by a company (or government), not by a bank and not for purposes of withdrawing funds.
Technically, Diggle was hired by Moira Queen, not Oliver Queen.