Its excellent practice if you hate your money and are a glutton for punishment, Washing a hot engine is disaster in many ways and then spraying with diesel fuel oil is a very very very sure way that your wiring/plastics/rubbers etc get dry and brittle and you end up crying in a corner at the most expensive and often repairs of your car.
If you want a clean engine, buy some engine cleaner and do it yourself. For wheelhouse cleaning, soak the mud with a non sudsy detergent cleaner and powerwash it away.
These stupid washing stations are there to fully destroy your car from every aspect.