The Glowing Army Elidibus summons, those were....
- the Warriors of Light from the rejoined shards, whose aether was merged with his (being the Heart of Zodiarc)
- summoned using his Creation magics, but branded as a result and thus bound to his will
- A gambit that heavily taxes his aether and is thus saved as a last resort. Also the reason Y'stola makes mention of a cacophony of voices, as overuse would either chnage Elidibus' personality or materializing this army comes at great risk of bring branded himself and thus being Zodiark.
- Also would include the First's WoL as a timey-wimey technicality (as there is a Timeline where that shard was rejoined and intersects with this one via the Exarch and Tower)
In other words, the army are comprises of Warriors of Light, fallen, yet reborn as thralls of Zodiark. And Elidibus had this power all along.