Just to clarify, John Harvey Kellogg is not the founder of Kellogg. His brother, Will Keith founded the cereal company. John Harvey owned a sanitarium and advocated all sorts of kooky things, mostly “health” related, as broadly as that term was considered at the time. IIRC Will Keith didn’t seem to share a lot of his brother’s beliefs but was more than happy to sell the cereals his brother promoted as beneficial to his adherents.
Of course, a wealthy industrialist supporting racist beliefs at the turn of the last century would be pretty common, but I don’t know specifically about W. K. Kellogg’s beliefs.