During the Stormblood story cycle of Final Fantasy XIV, the "Return to Ivalice" raid series has combined the lore of the Tactics games and Final Fantasy XII into the MMO. In fact, FFXIV and FFXII just might be concurrent stories. Which brings up the question, could Elidibus from Final Fantasy Tactics be the same Elidibus as FFXIV's Ascian Emissary?
To figure that out, let's take a look at what we know of Elidibus in Tactics, first.
Elidibus, also known as Elidibs, is a legendary wizard said to be a hero of the Fifty Years' War. He possesses the thirteenth auricite and can transform into a Lucavi demon using its power. He' an optional boss who comes between the fights with Addrammelech and Hashmal.
In Tactics, Elidibus uses several powerful spells, including the move Zodiark, and the Magick City of Gariland is his hometown.
As for Elidibus the Emissary in FFXIV, despite appearing in the Seventh Astral Era quests, we don't know a whole lot about him. All we do know is that Elidibus is far less neutral than he initially claimed.
While there isn't much evidence to support the idea that the Ascian Elidibus MUST be the wizard from Tactics, the fact that both games share the same universe does make it a bit likely. That the wizard Elidibus uses a move with the same name as the god being the Ascian Emissary works for is a clue, but Zodiark, like many other figures in the Final Fantasy series, is a recycled figure.
It would also give both characters an interesting story arc. From hero to Lucavi demon to dark-aligned messenger, if both Elidibus' are the same, he'd have one of the most nuanced backstories of any FFXIV NPC.