I don't think there is a problem with metallic cable conduit grip. The problem is with the magnetic material used around single phase cable. Usually a bronze made grip is indicated. This is the same problem with conduit itself. If we will take the grip as a shield the build-up voltage even in short-circuit case will be negligible since the grip is short. The metallic conduit has to be well grounded at least all 100 ft.
Are you talking about Kellum grips for strain relief on vertical runs? No other reason to install 'clamps' in a conduit that I know of. Kellum grips are designed for individual cable use and are stainless steel mesh for strength. To my knowledge they are always installed on individual cables for uniformity of pressure on the cable insulation.
