Are there any applications UV-LED printing is not ideal for?

This depends on your inkset. There are a few items that are not suited well for UV printing.

If you use the LH 100 hard inks, then you probably want to stay away from leathers, soft rubbers, or silicon-based products with flex, bend, or stretch.

If you use the softer inks, you will want to steer clear from drinkware, as well as products that may be exposed to high moisture, humidity, or chemicals.