Yes. Using a dilectric union is a recommended practice. When too dissimilar metals (like copper and iron) come into contact in the presence of an electrolyte like water, an electrical current will flow between the two and the more anodic metal, in this case the iron, will corrode more quickly than it would if not coupled, and can ultimately lead to joint failure. This type of failure is often seen in water heater applications. A dilectric union separates the two metals with a gasket, preventing the current flow and resulting galvanic corrosion.