Although I might include those entities in the contacts for disaster recovery / contingency plans, I would not consider them a vendor. Simple definition, a vendor is someone who provides goods (forms, supplies, software) or services (core processing) to operate the bank.
While you could make an argument that the Bank and the Utility Customers supply a service, I just don't see them in the same context as other vendors.
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I hear and I forget. I see and I remember. I do and I understand.--Confucius