I swapped a stock weber carb with a nickerson/holley carb and I'm not sure where the fuel pump vent tube should be relocated. The weber has provisions for the tube, but does the holley?

Most Holleys don't. I installed a fitting in the air cleaner housing that will dump fuel into the venturi in the event that the pump seal fails. Do not use any of the ports on the side or base of a Holley for this as it could mess up your carb calibration by allowing air to be sucked thru the pump.

Some aftermarket flame arrestors (Gaffrig) have a nipple on them to attach it to.

Nickerson's did my carb...great job. As RedDog said Gaffrig arrestors have a nipple to stick the line on, at least mine does.

Thanks for the replies. I'm using a K&N spark arrestor so I'll have to fabricate a fitting that will return the fuel back to the carb.

K&N does sell such a part if you check it out