No he isn't. Despite similarities to the way Warlocks and Wizards manipulate the Void, the fundamental difference is that Warlock do so through their Light.
The Light is anathema to the Cis-Jovians, and Xur himself will tell you how it pains him.
English
-
He isn't a Cis Jovian for sure.
-
I was always under the impression he was a guardian born of darkness instead of light.
-
He's actually one of the first awoken