If I'm correct, they are compatible but only one way. The older variant of the ipkg format uses tar compression while the newer version uses ar. OpenZaurus (OZ) can process both versions of the format but Sharp ROM only deals with the older one.
So you should be able to install
any package on OZ but whether or not the software will run is another question. The Opie environment used in OZ is derived from Qtopia (what the Sharp ROM uses) but they are slowly diverging and compatibility is broken for many non-trivial applications. There is a Sharp compatibility package for OZ (sharp-compat-oz) that will help in many cases.
My advice would be to give it a try, you can always uninstall. And do check out OZ feeds
- there are over 2000 packages there already.