The whistleblower's claims are new, and that sort of by definition (since a whistle needed to be blown) means that the claims were not publicly reported beforehand, so support for this will take time.
That said, there have been prior collaborations between the American Beverage Association and the NAACP of New York to challenge things like Bloomberg's proposed "soda ban" back in 2013. AFAICT, no NAACP representative officially called the proposed ban racist, instead claiming an infringement on personal freedom, but they did note that the structure disproportionately impacted minority-owned businesses, quoting the linked article:
Mr. Bloomberg’s plan, the brief argued, would disproportionately hurt minority-owned small businesses, which faced competition from larger convenience stores like 7-Eleven that would be exempt from the soda restrictions because of a quirk in New York’s regulatory structure.
“At its worst, the ban arbitrarily discriminates against citizens and small-business owners in African-American and Hispanic communities,” the brief said.
It never says the word "racist", but saying a policy disproportionately and arbitrarily harms minorities is effectively describing a racist outcome without necessarily accusing their opponents of racist motives.
The same article also notes ongoing ties between the NAACP and soda companies, particularly Coke:
But the N.A.A.C.P. has close ties to big soft-drink companies, particularly Coca-Cola, whose longtime Atlanta law firm, King & Spalding, wrote the amicus brief filed by the civil rights group in support of a lawsuit aimed at blocking Mr. Bloomberg’s soda rules, which are set to take effect in March.
Coca-Cola has also donated tens of thousands of dollars to a health education program, Project HELP, developed by the National Association for the Advancement of Colored People. The brief describes that program, but not the financial contributions of the beverage company. The brief was filed jointly with another organization, the Hispanic Federation, whose former president, Lillian Rodríguez López, recently took a job at Coca-Cola.
This doesn't prove or disprove the whistleblower's claims; those outside the NAACP (and possibly the NAACP, I can't find a source) have fought restrictions on what food stamp money can be spent on before, unrelated to soda. There was a period in the last 20 years in which food stamp critics were claiming recipients were spending it on steak and lobster and either the selection should be limited, or it should be directly distributed as nutritional expert chosen food products, and that approach was criticized as paternalistic, if not downright racist, by various critics. The money Coke contributes to the NAACP is part of many charitable endeavors, and there's no evidence it's enriching the NAACP, vs. merely funding necessary expenditures for their charitable programs.
- It is publicly known that the NAACP of New York has opposed at least one specific soda restriction, and claimed the policy had a racist outcome (without explicitly accusing the proponents of the ban of racist motives).
- It is publicly known that they did so in coordination with soda industry lawyers.
- Coca-Cola specifically is known to have donated tens of thousands of dollars to a program, Project HELP, developed by the NAACP.
Whether the relationship was corrupt (the NAACP took specific actions they otherwise would not have to receive the money) or innocent (the NAACP's beliefs on personal freedom for food stamp recipients and the disproportionate effects on minority small business owners happened to overlap the ABA's goal of blocking soda taxes/bans) can't be proved without relying on the whistleblower at this time.