Why wouldn't a spark plug need a conductive anti-sieze compound? It goes
between the plug threads and the block.
The never-sieze compound is good stuff. The plugs in my motorcycles and
outboards seem to conduct fine.
I doubt you could really find any compound that would prevent threaded fittings
from conducting anyway. There will always be significant metal to metal
contact. The anti-sieze is to fill the microscopic voids where corrosion grows.