While I think it'd be cool to have skeletons spawn more right near fossils, I don't think increasing skeleton spawning in a single chunk would make it easier to find them. Skeletons spawn all over the place, and I doubt you'd be able to pinpoint a chunk where more skeletons came from than usual. You might be too close to the chunk for them to spawn there anyway. A solution might be to massively increase skeleton spawning in a several-chunk-large area around fossils, but that would probably confuse players who don't know about the easter egg.
I think it'd be best to just have skeletons spawn at fossils in order to make them more interesting, not really to make them easier to find. If you want the latter, you could just make them more common.