I have skied both sl and Gs race skis in bumps and I find the sl's are much preferred. Of course there are many versions of bumps, but for me a quick and med-soft ski works the best. Allows the most options on how to navigate. If the bumps are smallish and softer, and you want to ski them fast, then I could see a longer cheater GS ski being a good choice. A Gs race stock ski is not turny enough in the size I ski them (192 cm, 27m radius). I have to do all the work, the ski is along for the ride with me.
Bottom line for me is I usually avoid bumps when I have my race skis on, unless they are very soft. I did have a really good bump run this year at Sunday River on a trail with pretty soft bumps. I was on my sl skis, but the stiffness was negated by the soft snow. You can always do it, but it may not be enjoyable.
I took my sl skis into glades a couple of weekends ago to see how they do. They were double black glades with big irregular bumps. I actually had fun in some spots, but the torsional stiffness was too much and I would hook an edge suddenly sliding down a steep drop. I also dulled the crap out of them, and decided I needed a softer, more forgiving ski for trees. I bought a used MX78 to use for this purpose. I am a clyde, so the MX78 is a softer ski for me, although not for everyone.