I doubt seriously that the underwriter has a friggin' clue what an 'audited' financial statement even IS !
It probably isn't the underwriting asking for it. It is the 'front man' that gives the information to the underwriter. Some of them try to come up with as much as possible to give to the underwriter so they don't reject it.
I've written letters that basically says (1) the client keeps their own unaudited books (2) that I've prepared their tax return with the information they provided me and (3) I have no reason to believe the information they provided me was incorrect. That has always satisfied them in the past. I try to intentionally phrase it in a repetitive way to try to convey to the mortgage guy that he is an idiot.