Can I use Push-Fit fittings as a dielectric union?

Yes and no, it depends on the item. The standard BPF Brass and SSPF fittings such as couplings, elbows, tees, male & female adapters for example cannot be used as a dielectric union.

However, the Boshart BPF-FRC05NL and BPF-FRC07NL - No Lead Brass PUSH-FIT Flexible Repair Couplings with a 12" Stainless 304SS Steel Braided Flexible PVC Hose - are the only two push fit fittings that can be used as a dielectric union. Boshart does not offer SSPF series Flexible Repair Couplings with a 12" Stainless 304SS Steel Braided Flexible PVC Hose.