It is unlikely that he has any whistle blower protection.  Although most of Sarbanes/Oxley doesn’t apply at all to nonprofits, the whistle blower protections of Sarbanes/Oxley apply broadly to all organizations, including nonprofits, but only make it criminal to retaliate against a person who provides information to a federal investigator.  Sarbanes doesn’t protect against retaliation for disclosure to state or local governmental investigators, let alone for bringing bad news to a board of directors.  State whistle blower protection laws, where they exist at all, apply mostly to employees and sometimes only governmental employees. Assuming he is a typical volunteer treasurer, a state law would not normally apply to him.  His best protection might be from your organization’s own whistle blower protection policy -- if there is one -- that could create rights beyond those provided by the law.

From what your wrote, however, it doesn’t sound as though he has charged fraud, illegal activity, failure to follow corporate policies or other misfeasance of the type normally covered by a whistleblower protection policy.  It sounds more like he has raised a series of governance issues and some of the board want to make him a scapegoat for the bad financial situation.  If he is responsible for the bad financial situation, it may make sense to remove him from office.  If he is just the messenger, it is not one of the top ten practices of good governance to shoot him.