I don't see why not. Sounds like a good idea actually, and I should have done that to the RS9000's I recently installed on my Avalanche.
Just beware that if you spray laquer based auto paint on enamel (or vice-versa....I can't remember...but I think that's right) it can act as a solvent for the existing paint and cause it to crackle and peel off, ruining everything. I know this from an unfortunate experience and the resulting loss of hours and hours of prep work.
Just check with an auto body supplies shop and be sure. I THINK it's OK to spray enamel onto laquer OR enamel, but you CAN'T spray lacquer onto enamel. It's worth your while to double check this first.
Of course, if Rancho says their shocks are powdercoated, you could likely spray them with either.