If the controllers (or at least two of them) isolate the panel negative from the battery negative, the single switch should in theory work. If the controllers do not isolate the panel negative from the battery negative/ground, it will not work. I would go with three separate switches if possible, as switches are not all that expensive all things considered and there's no question that it will work and it gives you a little more flexibility should that need come up.
(A suitable fuse that can be pulled is also a possible disconnect option.)
