I would agree with John on being careful with the use of vinegar. While it's a decent cleaning agent, it also will lower the Ph of your soil and if your not careful, and the Ph gets too low it locks up the nitrogen in the soil making it unavliable to your tree. Another thing about ph being low is that many moss' and alge flourish in that environment defeating your purpose of using it. It's ok to use if, just be cautious and aware of the possible results. If your tree can be turned on it's side while you clean that rock so that the excess drips off to the ground so much the better.
I too would love to see a pic of your Sugar Maple. I've just started working on 3 of them to see how they perform and would love to hear about your experiences thus far.
Boaz, Kentucky US growing zone 6A