Casein is the protein in milk which helps reduce the effects of eating spicy food. Since most soy milks do not contain casein, I doubt it would be as effective as consuming milk or a dairy product.
i wouldnt think it would work as well since it doesnt have whatever regular milk has. but it should still help
I know this isnt an answer to your question but lemon juice has always worked for me:D
Only one way to find out, eat something spicy and test it. Then hope for the best. :D