If you literally buy the loan; i.e. your institution did not participate in the initial credit decision, then the borrower is not opening an account at your bank and does not meet CIP's definition of a "customer." (Purchased loans are also specifically excluded.) Thus, the regulation does not apply.
The hook is that there is a wealth of examiners who do not comprehend that.
Consider too, verification of the borrower's identity reflects on the value of the credit; it's just a good idea and it would be smart to have evidence that it was done. Prior thread.
If you would require a resolution for a loan you made directly, I suggest you require a copy of one here. However, the resolution is not a CIP issue.