Cr123 batterys are stacked all the time in torch lights. I myself have 3 torch flashlights that run on double and tripple stacked cr123's
I have also ran stacked cr123s in my magneto with good results.
You need to make shure your coil does not draw more amps than the batterys c rating and you will be,fine , also make shure you have a atomizer with a,high enough resistance for 6v if you are useing a mech
On a vamo though you should be fine. If anything happens it will simply short out the vamo rather than over heat or short your batterys, the vamo should have built in protection
Running stacked cr123s in a mech is verry common practice in the flashlight world. you just need to charge them together and discharge them together and also,rotate there positions in the stack after charges. Watch the amp draw on your device and dont over work them and nothing wil go wrong . Cr123 batterys are the most commonly stacked battery in the world