UNX works against what ever database you design against. Performance is based on back-end, in this case ECC. If ECC is slow and contains transactional data, the response may be slow. Keep in mind you are NOT extracting data from ECC, you are just creating a metadata layer over ECC so users see a more friendlier interface.
I don't understand the question about licensing related to IDT. If you have BI 4.0 you can create UNX, users would be using WebI to view / edit or create WebI reports.
Regards,
Ajay