User blog comment:Victory awaits/Zachariah`s rank?/@comment-26982641-20160809204900/@comment-1975828-20160810025456

Saying any of these angels are Seraphs is still speculation. It would lead to an edit war if you tried to add it as fact.

All that's certain about Zachariah's rank is that he was Castiel's superior during his lifetime, and during that time, Castiel was a regular angel, who may or may not have been a garrison leader.