I can remember how things changed from one Hong Kong show to the next. First show ..a few strands of natural colour akoya tucked apologetically to the side and incredibly cheap. Next show...bosh...lots and lots of natural colour pearls with soaring prices. Japanese sellers had spotted that...
That can also be a burr when the two drill holes don't quite align. With a cheap drill bit it will bend just a fraction, not enough to break but enough for it to go out of alignment. This happens when the pearl is rounded so the tip skids just as it touches and before it bites into the nacre.
The dremel would be fine for enlarging holes (personally I use a simple hand-held ordinary domestic drill for that) You only really need a 'proper' pearl drill when full drilling as lining up the two halves would be very difficult and fraught with the chance that they will miss in the middle.
I...
They've been around for a couple of years or so. It's another Grace thing, along with dyed pretend Tahitians, mostly around 10mm (which look quite good from a distance, well matched strands with even some peacock-ery). (plus of course the dyed gold south seas and the dyed purples
Not my expertise but would not a diamond drill bit in a drill (handheld or otherwise) not be a better plan? What you need is what drilled them in the first place. What drills a diamond?
I never use reamers.