Yes—the Canon 580EX is generally considered safe on a modern camera like the Sony NEX-6 from a trigger-voltage standpoint. The real danger is mainly with some much older flashes, which can put several hundred volts across the sync contacts and damage electronic camera circuits.

Modern flashes from major brands typically use low trigger voltages, often in the roughly 3–6V range. Community reports mention Sony support citing a 24V limit, while some photographers treat anything above about 5–6V as a caution zone for digital cameras. Either way, the 580EX is a modern Speedlite and is not in the class of old high-voltage flashes that are known to cause problems.

If you want to verify a flash, you can measure trigger voltage with a voltmeter across the flash foot’s center contact and the ground/side rail while the flash is charged and ready. But for a 580EX, voltage is not the main concern.

Separate issue: physical and protocol compatibility is different from voltage safety. Even if it’s electrically safe, you may still need the correct Sony-compatible adapter/trigger setup for it to fire or communicate properly.