I'm just guessing, but I wouldn't think that would be a problem. The tomatoes would probably keep the level of MR spores high in their spot, so it wouldn't matter if there were few spores "next door" in the kale patch.
If you till heavily, I wouldn't expect the "dilution" of spores to hurt the tomatoes any. Since they multiply once they connect to roots and invade them, the tomatoes probably only need enough spores to "inoculate" them.
I think I've seen reports that roots acquire fewer MR when there are few spores in the soil, but I wouldn't think that "diluting" them by tilling and mixing the tomato's soil with the kale's soil.
I WOULD worry if articles were saying that one kind of MR competes with or suppresses another. But I never heard that.
I wish someone who knows more about it would chime in!
