Spartan for example specifically advises against this. Those screws in Spartans are specially made of the same alloy, 85-5-5-5 bronze as the rest of the seacock. There is no such animal as an 85-5-5-5 bronze grease zerk thus installing one introduces dissimilar metals into the equation... They also strongly advise against using that screw for bonding. They are drain plugs for intended winterizing..
MS, could you use the grease zerk, grease the valve and then remove the zerk and put the screw back in?