Sourceberry is not tagged as a fruit and so it doesnt get recognized by other mods as fruit.

Which mods are you talking about exactly? I don't see a fruit tag included in forge, so we'd need to know which one they are using, assuming it's a shared one.

Most crop mods and diet use forge:fruits/fruitname. You can check croptopia, harvestcraft or diet for examples.

Ok, i checked. That's true for harvestcraft, while diet use another one and they included many fruits from another mods themselves, croptopia uses yet another tag that seems to belong to another mod (why so many different tags <.<).
I've added it to forge:fruits/berry to my open PR #522 so it should work for few ones.
Consider opening an issue in Diet to make them add the berry, since they seem to accept that kind of requests.