The only way to know if they are safe for pono is to know how the cables are wired. The pos and neg wires for channel A must be entirely isolated electrically from channel B. There are tech papers on the pono website (see attached) that explains bal mode and the wiring needed. It is unique wiring configuration and off the shelf stuff won't work.
Don't use pono in bal mode unless you are certain the wires are correct or you could brick the device, blowing all 4 amps.
I don't know what kind of jack is on the end of the cable. You would have to have headphones with the channels wired separately. If your phones are designed for bal and have an xlr plug and the jack on that cable is xlr then the cable will work BUT ONLY IF the wires go to the plug contacts in the correct configuration. You can't tell that by looking at a picture. You need to trace the wires. Some stuff sold on ebay say sit works bal on anything--that bull.
If the cable is specifically designed for pono and no other device, then it cam work. Contact the cable maker to be sure. On the ebay store for this seller, it claims that it has a cable specifically made for pono based on the pono tech sheets--if that is true, and this of one of those cables, then it should work.
http://www.ebay.com/itm/Pono-Player-Headphone-Cable-Balanced-4-Pin-XLR-Adapter-/171600336189