Haven't encountered Nael myself, and yes Cid has a Hyuran model, but Nero is definitely an Elezen model with a different head attached. Look at his emotes, and his basic stance, and compare his height to other characters. (He makes Cid look ridiculously short by comparison.)
It took me a while to work that was the case, but ever since he showed up in the Crystal Tower arc I was thinking that Nero's head doesn't quite look like it fits his body - and that would be because it actually doesn't. It's not so obvious with the Garleans wearing their usual bulky armour, but Nero's "civilian clothes" make it a lot more noticable.
