As long as you generate all the chunks you want in Sponge and then don’t generate any new chunks in Bukkit, it should be OK. Chunks unloading should not be an issue. I haven’t tried moving a Sponge world to Bukkit though, so I’m not sure what else might go wrong.
There is some work going on to make Bukkit plugins compatible with Sponge, but it’s got a long way to go yet from what I’ve seen. **Discontinued** Pore - A Bukkit-Sponge Bridge - #306 by jaw818