it would only be 5 points of damage. Other bonuses to damage don't apply, per the rc.
But still, as other's have pointed out, if you hit about half the time, then that's about as good as a feat that adds +5 to damage.
But you do have to use a scimitar, of course. A warhammer gives +1 damage per [w], while the scimitar's high crit is only a flat +0.5 or so (pre-mastery). So on a many [w] attack, a hammer would still be better (and you'd save a feat.)
you could compare to getting +1 to hit with a longsword, too. The same idea will apply: For high-damage attacks, the longsword will be better.
But of course, rangers don't get a lot of high-damage attacks. As a result, scimitar dance is quite nice. Go drizz't!