Howdy K. I've used Glen Boulder to access Gulf of Slides for some turns, but never Oakes Gulf. Times I've dropped into Oakes have been from the north (off Mounts Monroe and Franklin, and from east of Lakes of the Clouds), and once from Boott Spur
I think you could use Glen Boulder to access Oakes in theory, but Boott Spur would be easier. If I recall correctly, the area west of Gulf Peak (above, but on the same ridge as, Glen Boulder) is heavily treed.