The "Dread Guard" gear has existed on datamining sites like Torhead since 1.2 (Explosive Conflict) came out. It was called "Denova" gear. "Denova" gear gives identical stats to "Dread Guard" gear. Its pretty obvious that "Denova" gear was originally meant for Nightmare EC, just look at the name. NEC never came out though, so you just changed the name and moved it to HMTFB instead.
Denova Survivor's Boots
Dread Guard Survivor's Boots
Could EC and TFB have "always intended to share the same appearance"? I guess. The gear we got though was intended for Nightmare EC.
Also, EV and KP gear shares appearance because they both drop the same set, Rakata. There is no precedent for two tiers of gear from different Ops looking identical.