3rd party programs, even client-side, can be detected, and that includes modified textures etc. If the developer cares for that, that is. In that case they also need to inform the player that they are monitoring their system in whatever degree is necessary for their detection tools.
As for FFXIV...I doubt they care so I highly doubt they do it. Outside of highly competitive games, it's just really pointless to waste any resources on such security, especially since it is not without its performance cost. Realm Reborn was made partly with reducing the system requirements in mind too...It's just that it's not impossible unlike people seem to think.