well it is dishonest in a sense. People buy those official umat papers thinking that it will boost their performance in umat. ACER don't specifically mention anywhere that it will help; people just make the assumption that it will help. Interestingly they do mention that they do not encourage other thingos like medentry etc, which would lead the average person into thinking that their product is superior (once again, without explicitly mentioning it).
The assumption that past papers help is a reasonable assumption to make right?
Essentially they're making more money off people based off peoples false (but reasonable) assumptions.
Which is equally understandable, because they dont want you to have practised anything that could affect the final distribution of results. Psychologists lie to their subjects about the purpose of their experiments for similar reasons.