Even though I've purchased FFXIV:ARR though Steam, is it possible to play the game though the non-Steam client?

I've heard some horror stories on the Steam forums and Reddit. Is it true that if I want to play the non-Steam version, I need to purchase a new copy of FFXIV:ARR through the SE store? I have been looking forward to ordering the physical Heavensward CE for weeks, only to hear that Steam doesn't accept codes or keys from the SE store. Should this info be correct, I'll never be purchasing content through Steam again.

So, if there is a way to play this game without Steam or purchasing a second copy, please let me know.