I don't know if they all are or not, but I've got a wild cherry tree growing with a bunch of black walnut trees.

I had the same thought, the shade and competition for water and nutrients would be a problem even if the walnut wasn't poisonous. Wild versions of all kinds of cherries both orchard and flowering are mostly short-lived trees that pop up in clearings, grow quick and bloom (and fruit) heavily before the forest comes back and a new set of trees takes over. They do not like to be shaded or among larger trees. Shading from nearby taller objects can even worsen their disease problems, by keeping them damp.

I have no experience other than to say the black walnut I have has had no apparent effect on the chinese elm growing next to and over it.

If you are wanting to plant the cherry under the drip line of a full grown black walnut, or next to a young tree that will grow to overshadow the cherry, it probably isn't a good idea. Whether or not the juglone bothers the cherry will probably be minor compared to the shade and competition the walnut will give.

If you are planting where it will be a bit outside the drip line of the tree, or with a small walnut you will keep the walnut pruned small, then you will probably be OK with the cherry.

Most chemicals, juglone included, work best on seedlings and small plants. Once the plant gets established it usually will have the capacity to survive the chemical onslaught. It may not flourish, but will survive. Thus walnuts use shade and competition for nutrients as additional weapons to protect their domain--kill the competition when it is small, then starve it forever after.

BWs weren't common in south AL where I grew up, but there were two in my grandparents' backyard - the only two on the 250 acre farm, so far as I can recall. No fruit trees were planted anywhere near them, until as an unwitting 8-year-old, I planted a couple of pomegranates I had rooted from cuttings about 20 ft away from the then still fairly young BW. The poms grew OK, but never fruited for nearly 25 years, until trenching to install a new septic line passed between the BW and the poms, which all but killed the BW. The poms exploded into fruit production and have not missed a lick since.

I am by no means an expert, but I don't wonder if culture might be part of the different responses about juglone and plants in the vacinity of BW trees. Do you clean up the leaves each year, or let them rot in situ? Maybe that would mean more juglone. How about the walnuts? The husks and shells have the most juglone, I think I read somewhere. I clean up both around my BW trees. If we didn't have such a small pallette of trees around here I might be willing to take them out, but a tree is a miracle around here. I don't know how old my trees are, but they are at least a foot in diameter at the base and as tall or taller than my hundred year old two story house. The natives around here (including the lady who lived in this house for fifty years and presumably planted these BW trees) don't do a lot of lawn watering, so trees have to survive on less water than they might like, so I don't know how old these BW trees are. I'm sure they don't grow like they do in the east. I bought a cherry tree (Meteor) and it is planted next to but not under one of the BW's. It gives us plenty of cherries for jam and pies and freezing, and so far has given us no cause to think we planted it in the wrong place. It is west of the BW, so the early sun is maybe blocked, but gets sun most of rest of the day. I think there are a lot of variables that aren't mentioned that might mean success or failure with the planting of your cherry tree. If you want trees around here, you have to water. If you just water the cherry tree, then that will send the BW roots over to where it can get water, which might encourage a bad competion between roots. Roots go where they can get water. So your question is maybe a hard one to answer without more information.