The Guard Scorpion was also the first boss in Ala Mhigo. To say nothing of how Nael van Darnus was essentially Sephiroth (grey hair, wields an unusual weapon, is a high ranking supersoldier that went insane, summons a 'meteor' - even had a 'walking into the flames' scene).

Ironically, because of FFVII's iconic status and the success of it's tie in games, I doubt we'll ever see an actual crossover event here in FFXIV, as such events or content seems to be used for cross-promotional purposes (hence why less successful FF games like FFXV got crossovers).