This would be essentially along the same lines as "porting" pdaXrom srtuff, it appears.
If by port you mean converting from X11 to using the framebuffer, then no not at all.
If you mean fixing the 'broken' control files in pdaXrom ipks then yes, similar (but I'm not sure if this is the (only?) fix which must be applied to the pdaXrom ipks).
Will any of the xrom stuff work on a 5500 (if correctly dissected and transplanted)?
A qualified no: PdaXrom apps are compiled to arm5 code, the 5500 can only run arm4. You may be lucky and find an app which doesn't have any of the new arm5 instructions. Probably (almost certainly) not though.
On a 5600/Cxxx they would work (assuming you fix the control files and grab the dependencies and probably use GPE, unless you're after a command line app)
Si