Hi Bonfield Bushwacker,
Your report is disturbing to say the least. I think that when incidents like this happen to individuals or groups they should be reported immediately, and even perhaps demand your hard earned money back. If everyone started demanding money back from every illegal ATV/motorboat use/incursion into one's solitude in Algonquin Park, Ontario Parks would have no choice but to react to the threat. Else if we do nothing, nothing will be done to curb these disturbances.
I share your concern, and see no reason why someone else's mechanized transport(illegal or otherwise) should be allowed to impact your enjoyment of the interior of Algonquin Park.
I recommend you fill out the back of your permit and submit it to the access point you entered/exited.
Also, check out the impact section on the ABR(Algonquin Backcountry Recreationalists) website.
http://www.ABRweb.ca/Impact.htm
There you can download an ABR incident report form.
Mark Rubino
Mark's Algonquin Park Sampler - Blog
Mark's Algonquin Park Sampler
http://www.ABRweb.ca .. Algonquin Backcountry Recreationalists - Caring for Algonquin's Backcountry