rob:

I believe you will find all the sour cherries are self fertile. The ants are probably collecting nectar from the blossoms. I see them working melon blossoms all the time. But I think they are poor pollinators.

They are self fertile, but that doesn't mean they don't benifit from insect pollination does it? I don't mean to imply that I know they do....perhaps light breezes are enough.
I certainly don't see much pollen on the ants themselves so I suspect your right.
A quick internet search didn't turn up much useful so I doubt they are a significant pollinator but I was curious after three years seeing them.

Just a thought, but ants seem to stick to a single crop, so they may be up one tree but not the next tree over, so I'd think it might self pollinate yet be completely useless in pollinating between trees.

As well- bees collect and transport pollen and I'm not so sure ants do the same.

I agree, ants couldn't be a very effective betwean trees...without wings they just don't cover enough ground. My only thought was that as they worked the blossom for nectar they might disturb the anthers enough to dust the stigma...they look kind of clumsy in there!