Ok, quick update...

gimp seems to respect the printing preferences properly, not only the settings for my photo "queue" but also, which printer is actually default.

Doing some rpm -q --requires on both packages show they both use gtk for the GUI toolkit, and the printer dialogs being nearly identical, I assume it's provided by the GTK toolkit. 

This seems to indicate the problem is with shotwell, not the toolkit.

Haven't tried actual print yet, the wife already shutdown her laptop for the night. Will try tomorrow.

Thanks,
Richard