Yeah, I can see using the felt-tip for a spot. It would be kind of like using retouching opaque and a fine (0000) brush. A light touch to the spot on the film, and then retouch the print.
I'm just not sure how the felt tip would work for a scratch...hmmmmm... how would you get the tip fine enough like you can with a pencil by pointing it on 400 grit wet/dry sandpaper?
They taught us to expose the graphite back about 3/4-inch or so, and then holding the pencil at an angle, to scrape it in a rolling motion to get a nice long tapered point about 1/2-inch long. I actually mastered that part! Unfortunately - they didn't grade for pencil pointing...
The tricky part then was to come down at a 90-degree angle at the correct pressure to leave a dot of the density required. I have also seen people who are really good (like the professional I use), who can fill a scratch with little strokes so that you can't see it unless you're right up on the print and looking for imperfections.