FrankR, I don't know if this will help, but my whole body was (and some still is) covered in the kind of rust you are dealing with on your hood, maybe even worse.
Before even attempting to apply the rust dissolver I sanded as much of the panel right down to shiny bare metal as I could using a DA and by hand. I found that on many panels there seemed to be a lot of the original black primer even under the coating of surface rust, and I had to get through that in order for the rust dissolver to really take effect on the metal underneath.
I am no expert but from my experience I don't think rust dissolver alone can ever replace sanding as much of the rust and paint/primer off as possible first. I rely on the rust dissolver only to treat the pitted areas and to get the sanded panel clean of all and any corrosion left before filler and primer.
It sounds to me like you might want to go at that hood with a DA and get as much of it right down to the metal as you can, applying the rust dissolver afterwards to remove anything left. I'm not sure that a scotchbrite will do it.
Roger is right, if the rust isn't too heavy wire brushing should also work, but I prefer using a DA. Roger also mentioned it can take quite a few applications to get it all.
I've never used the spray, but a thicker brush on rust dissolver or naval jelly might also work a bit better.
Hope this helps, I feel for ya! It's a lot of work!