Here's a list of ULEZ exemptions [1]. I don't see any mention of delivery vehicles or luxury cars.
[1] https://tfl.gov.uk/modes/driving/ultra-low-emission-zone/dis...
[1] https://tfl.gov.uk/modes/driving/ultra-low-emission-zone/dis...
Taxis are exempt, despite plenty being diesels older than even euro 4.
Plenty of delivery vans with significant emissions are de facto exempt because the fee is negligible when compared to other expenses.
If the fee was at least a percentage of income/revenue or a percentage of the value of the vehicle, it would be a bit less bad. If it also scaled measured emissions by passenger instead of using the flawed emission standards, then it might even become useful. If it also included free vehicle replacements funded with revenue from the taxes on the excessive cars, then it might even be good.