Mad_Jock, you can get Dutch Roll in any configuration of aeroplane - the Chevvron 2-32c for example which is a straight wing microlight motorglider DRs constantly, albeit with too small an amplitude to be more than mildly irritating. The flying flea family all have DR problems, and all are straight wing.
(It is true that some swept wing aeroplanes have or had Dutch Roll problems - the SHAR particularly springs to mind and there's that infamouse Tu154 video...).
At my flying club we had a PA38 tied down to 3 large concrete blocks. In a storm it got airborne on its own and cleared a 10ft hedge. It is widely rumoured to be the best rate of climb ever achieved from a Tomahawk.
G