The wiki suggests even the gods don't know their identities (not really sure how that works). Will we ever know is or is it one of those things that will be intentionally left a mystery (like how Aroden died)?
The gods almost certainly know their identities :)
As for us mere mortals, while the Deceemverate's identities have been traditionally kept extremely secret, over the course of the Pathfinder Society campaign multiple of those individuals have been revealed (I believe 5 or 6 at-the-time active Decemverate members have been 'unmasked' over the course of various scenarios, though most have since left the position.
In fact, right now one of the ten current Decemverate members has chosen to officially reveal her identity to the world: Eliza Petulengro. Currently the other nine members are continuing to keep their names and details a secret, but as the Pathfinder Society campaign continues it is quite possible that some of their identities or details may continue to come to light.