Reg O 215.4(e)(1) states: No member bank may pay an overdraft of an executive officer or director of the bank...unless...

Does this only apply to overdrafts on accounts owned in sole or joint ownership by an EO or Director? What if the EO or Director is Guardian, Custodian, or Signer on the account?

This prohibition does not apply to the payment by a member bank of an overdraft of a principal shareholder of the member bank, unless the principal shareholder is also an executive officer or director. This prohibition also does not apply to the payment by a member bank of an overdraft of a related interest of an executive officer, director, or principal shareholder of the member bank or executive officer, director, or principal shareholder of its affiliates

I read that in the regulation, but that doesn't address my question about the EO or Director being in a less-than-ownership capacity on an account. I know related interests and principal shareholders are exempt from this.

Guardian, Custodian, or Signer on the account?

In this circumstance, based on the specifics of the relationship to the executive officer, the underlying account would most likely belong to a related interest.