In Zak V2 (en), the keys <U> and <J> should allow to navigate in the inventory and <I>, <O>, <K> and <L> should select objects.
It works in DOSBox, but not in ScummVM 1.1.0svn42826 on OS X 10.5.7.
The verb keyboard shortcuts are operational, as is old load/save dialog with <Shift>+<F5>.
I'm not far enough in the game to evaluate the other function keys.
The keyboard shortcuts for the verbs were hard coded in V0-V2. Seems that also the inventory arrow keys and inventory objects had such hard coded shortcuts - the primary reason we don't support those is that we weren't aware of those :).
Fixed in SVN