It's not mod use but just a normal part of development - when testing games graphic components may be hidden or not included to assist with checking animations and main graphics display correctly, and it's clear this screenshot is taken from an early test build of that fight.

Also things can change without warning at any time during development and so screenshots and trailers may not always be 100% representative of how things finally turn out in game - an example of this was back in an ARR patch main scenario screenshot that was on the Lodestone that showed the Syndicate in Ul'dah with Godbert clearly seated at the table, yet the actual scene in the game when the patch went live, Godbert was suspiciously replaced with a generic Highlander wearing a hooded robe in that same scene. It's just how game development is - things can change without warning.

The aetherotransformer SE considers an essential component of the MCH Job so that's why you can't hide it yourself normally, irrespective of how players feel themselves about it. For whatever reason the development team did in that scene, probably to assist with checking the animations of the character models or something in the battle as I mentioned. Either way, it's not mod use at all, but clearly an early build of that battle with character models having graphic components hidden for testing purposes. It's not representative of anything further.