In a secondary panel, are grounding and neutral bus bars required on each side of the hot bus bars?
I think you may be over-thinking this. You can make a connection on either bus without reaching across an ungrounded bus in that panel.

The ground and neutral bars are so located as to give you free access to them without have to reach around or near an energized bus. You could stand to the right or left to make your connections without reaching across the phase bus. 

In a larger piece of switchgear, the phase conductor bus should be located further in and the ground and neutral bars closer to the access panel not the other way around.

I think that is the intent of the code.