Gap does not cause flutter, slop in the linkage causes flutter. Gap causes control surface ineffectiveness due to air leak between the fixed and movable surface.

Before you say "I've seen fullscale with huge gaps" consider the type of airplane. I think the Kitfox had detached ailerons, but they are really suplemental movable wings that influence movement about the roll axis.

So, just to be safe all around: Seal your gaps, and make sure you have a TIGHT and SLOP FREE LINKAGE (that is from the control horn clevis through to the geartrain of the servo).

Jon