Does Soy Spray foam support mold growth?

No- closed cell soy spray foam does not support mold growth because it is a perfect air barrier.  Air (and thus moisture) cannot penetrate the material so you never need to worry about moisture-laden air condensing on the exterior wall sheathing or roof deck.  Cellulose will absorb moisture but is unlikely to grow mold because it’s treated with boric acid as both fire and mold retardant.  Although “Open cell” soy spray foam is hydroscopic, it does not support mold growth because it blocks the air that carries mold, so spores cannot enter the material, and the foam itself is not a food source for mold growth.