He's definitely a Hyur. Van Darnus is an Elezen, so it's farily easy to pick the two body-types apart when they're seen in-game. Secondly, "certain" channels may or may not have found out that he has the animations of a Highlander in-game. Just sayin'

If I had to place a bet, I'd go with Van Baelsar being a Hyur "highlander". It does seem like the Hyur have a low standing in the imperial military, however. All the centurions are exclusively Elezen, where as the bulk of their standing army is comprised of Hyur (mainly), as well as Miqo'te, Roegadyn, and Lalafellin. I've yet to see an Elezen legionnaire. Plus Van Darnus is noted to be of a noble lineage, and he's Elezen. Tie that together with the fact that all the centurions thus far have been Elezen, and I think it's safe to assume that the Elezen are dominant in the empire. However, it's highly possible this is just a coincidence, and that race does not matter within the empire.

As far as Van Baelsar's armor goes, it seems safe to assume all the Legatus have custom-built, but similar-in-design suits of Garlean armor. If you remember back near launch, it was stated that the Garleans have incredibly strong armor, capable of deflecting bullets with ease and heavily resisting magical attacks. Chances are most of the footsoldiers have the bare minimum, with centurions having slightly better armor, and the Legatus' naturally having top tier equipment - hence the underlying similarities between Baelsar and Darnus.

Each seems to fit their "duties", in my opinion. Darnus' armor is fierce, and seems fitting for the head of one of the empire's most valuable legions. They're a powerful force, and his persona radiates that power.

Baelsar on the other hand definitely has more of a scholarly-vibe in his attire. Even the brief glimpse we had into his mannerisms seemed to speak heavily on his duties as a viceroy. He seems to be more of a political mastermind than a die-hard warrior, albeit a politician who can kick some serious ass when the situation calls for it. He most likely spends a majority of his time managing Ala Mhigo and making certain there are no uprisings within the city - as a small scale rebellion could easily grow out of control.