I looked at the Zerg Origins.

The original zerg species was discovered on the ash world Zerus, in the center of the Milky Way Galaxy, by the xel'naga, a mysterious and ancient race of extragalactic geneticists, after they had abandoned their first experiment, the protoss, on Aiur. The zerg organism was a small, larval organism
Here: http://starcraft.wikia.com/wiki/Zerg_history

I doubt it was the voice in the darkness that they used.