Your question is not clear. A dielectric is just another name for insulation. Plastic insulation on a wire is a dielectric. The insulation between the two plates of a capacitor is a dielectric. What exactly are you asking?
Yes, you use a dielectric coupling. It is a coupling with insulation in the middle so the two dissimular metals do not come in contact. When two dissumular metals touch a small voltage is generated and this in turn causes a small current. The result of this is electrolysis or basically the same thing as occurs in electroplating. In this case we call it corrosion.
Each combination of dissimular metals in contact produce electrolysis to a different degree depending upon the combination of metals involved.
I see you are a pipefitter by trade. I bet you have a pipefitting book that will give you an exact answer for the combination you are using. Frankly, I don't have a more specific answer for you. I know in gas fitting we fit brass and copper to black pipe without a dielectric coupling without any problems. But, water in the pipe instead of gas may change that.