Can a standard Streamlight Scorpion (takes two CR123) accept a 18650 rechargeable battery? I was looking at getting a EdisonBright EBR34 3400 mAh battery and charger for my scorpion. Thanks Joe

If it is the standard xenon Scorpion then technically yes an 18650 will sort of work (assuming you can fit the larger battery into the light,) but it will likely be incredibly dim and could actually damage the bulb over time.
You could try using a pair of rechargeable LiFePO (but not lithium manganese or lithium cobalt!) 16340 batteries which are much more likely to fit and will be much closer to the lamps rated voltage -although still a bit higher when freshly charged so there is a risk of burning out the filament.
If you have extra bulbs laying around it might be worth trying but peronalIy I would just put the money towards a new light.

Thanks for the reply, it's actually a LED version, I believe the Scorpion X. I'm not sure if that matters or not

Using an LED definitely changes things, instead of needing roughly 6 volts to run the lamp the Scorpion X likely only needs a little over 3 volts and will use a regulator to shed the extra voltage. You will still have to deal with trying to fit an 18mm diameter cell into a space designed for 16mm cells, but other than that it should work.

Thanks for the help