Another thing that came to mind earlier today that would in my mind solve the cherimoya/atemoya question is this: if pollinated by its own pollen (and bagged to exclude any foreign pollen) and the seeds planted out, leaf shape alone in the progeny would tell us if there's any squamosa genetics or not. I'll get a separate brush and pollen container for doing Dream pollination this year, so we should have results this time next year.
If anyone has Dream seedlings, that'd be great to see pics, but if we aren't 100% sure of the pollen parent we couldn't call that conclusive evidence.