To answer your questions directly:

1. Ish. My axe motor does this on my middleweight I think but not by very much. I would prefer the pinion gear to be wholly on the axe motor itself since I don't really want to end up bending the shaft.

2. In my experience, no, not on a drive train but keyways do help lock in a gear or a wheel hub onto a shaft. The axe motor I have on my middleweight has a small keyway which I drilled a specific point to allow the grub screw to sit in. Depends on how much force is likely to go through it. In the lighter (i.e. Beetlweight) classes, I don't bother with this and simply screw the grub screw onto a flat on the motor shaft.