A smooth hard steel pick should be fine and maybe better than a corroded copper opr soft iron pick. Although I do confess to be mystified about what vent picks are for, except for poking a few grains of powder in when I forget to charge the gun. Then it's fill the pan, tilt the gun, poke, poke, poke, poke, spill, refill pan, repeat till I finally have enough to make the gun fire with a sound sort of like "spoof".
What horrifies me is when I see some hand-forged, square, tapered object that looks more like an awl or ice pick marketed as a vent pick. A few uses of one of those and a fella would have more flames coming out the touchhole than the muzzle.