I think the biggest problem will be not with the coral-like (coralline?) life forms on the land, but rather with your "aeroplankton". One of the defining characteristics for plankton is that they're neutrally buoyant in the water, and it's really hard to be buoyant in air. Interestingly, making the air moist actually reduces its density- water vapor is lighter than the nitrogen and oxygen gas that makes up most of the atmosphere, so when it displaces those molecules the parcel of air gets less dense- problematic because we're trying to make things float in it. I can't think of a way that biology would make this buoyancy happen, and I can't think of a reason evolution would select for it; there's not a lot of nutrients in the air, and it wouldn't keep you safe from predators.
However, if you're happy to explain away the aeroplankton, then I can't think of a reason that the land corals couldn't exist. You've resolved their biggest problem, desiccation, with the mists. They'd have to be euryhaline (able to tolerate a wide range of salinities), because the water splashed on them from the ocean would be salty and the water in the mists and storms would be fresh. They'd still be able to form symbiotic relationships, either with the new photosynthetic aeroplankton or the classic marine phytoplankton.
So, why don't we have land corals? I think they just aren't very fit organisms for land, where food doesn't usually come swimming to you like you have in the ocean, so they might be outcompeted by some kind of non-sessile version. More importantly, our air isn't nearly damp enough to provide life support. Corals are constantly exchanging compounds with the environment, and that includes bringing food as well as taking waste and reproduction away. The mists on our planet aren't dense enough to carry those, and it'll be a challenge to make that happen with fog.
Buoyant aeroplankton are hard to make, but if you're okay with that then land corals are certainly possible. Their biggest problem would be the harsh environment, not finding food.