Yes, it is. The earliest recognized ZC was the "Browntop" DOHC non-VTEC. It was essentailly the same as the next generation's "Blacktop" ZC, except for the easily identifiable brown painted valve cover, a slightly different intake manifold, a vacuum advance distributor, and motor mount placement. After those two came the SOHC VTEC ZC, basically a D16Z6 with a few minor differences.

The three major ZC's came in different generations-

"Browntop" ZC= DOHC non-VTEC, 84-87, pre-OBD Third generation Civic
"Blacktop" ZC= DOHC non-VTEC, 88-91, OBD-0 Fourth generation Civic
SOHC ZC= SOHC VTEC= 92-95, OBD-1, Fifth generation Civic

Those were the most common useages, however not the only cars they were used in.