My 2010 690 Enduro has a Scotts Damper, but my 2008 690 SMC does not - and the SMC has much steeper rake / trail geometry. I have never experienced even a hint of headshake on either bike.
I just mounted a new set of tires (Metzeler Karoo T Front and Mefo Explorer Rear) on the 690 Enduro. The KTM Shop in Las Vegas who installed them is just off of the freeway. This particular freeway is grooved - man, the bike felt like it was waggin' / wanderin' around pretty good. It didn't seem to do that so much with the worn set of tires (same tires).