User blog comment:FairyRaven/Fairy Tail Chapter 365: Fairy in the Jail!, Review and Commentary/@comment-5598380-20131230042329/@comment-7418318-20131230125839

I'm not convinced that Hades really "created" anything. The moment he stopped channeling the Demonheart's magic, the things disappeared.

Also those "Demons" looked a lot like the ghost-like things that Jellal created to attack and try to restain Erza with and the tentrils that Ultear wrapped around Jellal when she took over his mind.

For those two reasons I think he was just giving his (or the heart's) magic a temporary form, rather than creating actual Demons.