Hi! So if I understand your question correctly, you want to use a different label in the UI, based on the folder the image is in?
The approach you describe make sense and you can achieve this by overriding the default recipe config (which also defines the labels) on a per-tasks basis, using the key "config". So the data you send out could look like this:
{"image": "...", "config": {"labels": ["class_name_1"]}}
{"image": "...", "config": {"labels": ["class_name_2"]}}
This should definitely work if you're writing a custom loader – are you sure your generator is set up correctly and doesn't return/exit? You should be able to loop over multiple directories and then yield the images from them.