Yeah, he's either made of his element, or pure divine energy, like when he teleports, or when he gathers up his essence and releases it to make himself explode in MKD.
For the record, Raiden wasn't an Elder God in MKDA, he'd stepped down and become a regular Thunder God again, so his costume might have been fancier than normal, but he was still his regular self in a mortal form again.
We know that the Elder Gods' true forms look like the dragon in the MK logo, made out of glowing cosmic energy.
When you see them looking like giant see-thru blue humans, that's them taking on a form that allows them to communicate with lesser beings, similar to Raiden taking on a mortal form.
Granted that Shinnok, who was an Elder God, is also doing the same "took on a mortal body" situation whenever we see him. But he deliberately put all his Elder God powers inside his amulet, so without it, he's probably actually weaker than a lesser god like Raiden or Fujin. And he's stuck in that body now because he was demoted and banished to Hell.
Back to the subject of true forms, whether or not lesser gods also have the dragon shape, I dunno but I'd doubt it. He's probably just pure electricity or glowing white light, like I said.