Do you need one, no, the entire lower river from just above Maupin down to Macks Canyon is fishable from the road side. A watercraft just opens up the other side of the river, which gets less pressure because there are less boaters than car anglers. I think the suggestion to get your boaters pass early was in case you were thinking of floating Macks Canyon to the mouth, where most of the angling pressure is, and boaters passes are hard to come by in September.
Oh, and that 9 foot pontoon would be fine. The water from Sherars Falls to Macks Canyon is pretty mellow, with just a few minor rapids.
"Perhaps fishing is, for me, only an excuse to be near rivers." - Roderick Haig-Brown