Does an overdraft program tied to a checking account that is generally available to all customers, including Reg. O officers, at the discretion of the person opening the account, come under the purview of Reg. O. There is no underwriting associated with the overdraft program and the overdrafts are subject to a fee, not interest, and the fees are not waived for Reg. O covered officers. So, is the overdraft program considered an "extension of credit" under Reg. O?

Yes. See 215.3. Paying an overdraft is an extension of credit.