Dutch roll is characteristic of aircraft with stronger lateral stability than directional stability
Negative. DR can (does!) occur in any FW aircraft; it is driven by both lateral and directional stabilities, but is most noticeable where there is poor damping in one or both axes.
The ratio of roll to yaw (best observed by sighting along the wingtip, which will describe an oval) is approximately the same as the ratio of lateral to directional stability.
I've never seen an aircraft that didn't DR, but not many when it was a problem. A little bit of mild DR in a light aircraft is nothing more than an irritant (I can think of one which does so constantly, albeit with small amplitude), any undamped DR in a fighter is unacceptable because it prevents you flying an accurate guns tracking task. In an airliner you'd want it reasonable well damped, otherwise it'll make the steerage passengers airsick, but is unlikely to cause a safety problem unless it's very bad.
G