(SPOILER)No, he wasn't a deus ex machina. Hope was there anyway and Sazh just happened to be the pilot. If it wasn't Sazh in any of those instances then it would've been some no-name generic pilot who would've been ordered to deliver them to the final fight and catch them when they came back. Hope ship was near Sazh's the whole time too, your logic would mean that Hope had needed to have a Sazh clone flying his ship. His appearance may have been cheesy fan service, but he hardly did anything that no one else could've done.