Should be ok, as it is not in contact directly with the water column, BUT...thefatman said:however, the only needle valves i can find at HD are brass... ...will brass be ok?
if it is under the tank in a closed cabinet it will look like total H#!! in about 4 months . Find a better dealer with plastic needle valves, or just use a screw clamp on the hose to adjust the amount of air.
Sometimes a larger dial will help, try attaching a 2 inch dial to the valve to make adjusting it easier.