There is No "this style of lock". Our BLOCK lock is NOT a crossbar lock. They are completely different.
I did look up the "Kershaw Diverge" but only found the SOG Diverge which is completely open on all four sides. The plastic button does cover the thumb lock hole, but I would guess that it is for cosmetic appearances only or to make the injection molded plastic button easier to mount.
Secondly, and most important of all, blocking off the "gaping holes" means that in order to be effective at blocking all dirt and debris from getting into your knife, you would need to block off the largest "gaping hole" which is the blade slot that allows all kinds of dirt and debris inside of your folder.
The "gaping holes in the handle for crap to get into" should be looked at as gaping holes that allow your knife to be cleaned out much easier with compressed air.
Hope this helps. Let's Drink!
Jerry