I can only speak as a former Fury Warrior in Classic, but +hit while DualWielding is not wasted, yet 20% does seem quite extreme 
so gemming for even more would be puzzling, yet with a selected threshold of “9” it gems all crit in the yellow slots for me (using your import string).
I also just remembered that the threshold didnt work in classic for me, e.g. i was hit capped and still got Band of Accuria suggested.
Note for dual wielders
Auto (white) attacks have a higher chance to miss when dual wielding. Most people don’t worry about capping that. But if you do want to go for a huge amount of hit, we’ll let you do that. If your Melee Hit stat threshold is set to anything higher than 9 , we’ll assume that you want to reduce your white chance to miss as low as possible too."
So a treshold of 9 should work here…
It could be that your Hit-Gear has other Stats too that are better, but as i see it that isnt the case atleast for the Shoulder Slot.
Also since shaman gets 2 AP for 1 Str Strength Gems should indeed be prioritized.