(Beav is always online, just not always present - kinda like real life)
I think what you're seeing is normal. Holding one wheel while rotating (trying) the other will show the amount of play in each shaft and mating splines, not just where you can see but also inside where the stub and side gear fit together. Plus add in clearance of spider gears and ring to pinion. Adds up to a considerable amount.
Normally when you experience a vibration during acceleration it will almost always be caused by a bad or loose drive joint, whether a cv, detroit or a cardan type joint. High speed driveline vibrations are usually out-of-balance or bent shafts.
If you're still concerned have someone take a peek at it, that's better and cheaper than to repair it after it lets go. I can't tell from here.
(not cool - blind)
Beav