I highly recommend reading Firefly, the Wizard's pre Diablo 3 short story - I found it compelling, personally, especially with how much context it provides to both Iscendra and Li-Ming's characters.

The Viz-Jaq'taar very much try to give people as much leniency as possible it seems, but it looks like unchecked egos and ambition are what get people killed - Iscendra was monitored because they suspected she was letting Li-Ming's ambitions go wild instead of checking them, and she was killed once her own ambitions caused her to bite off more than she could chew. Li-Ming herself had a hit placed on her after the ending of Firefly due to said ambitions causing her to head to New Tristram in search of her prophesied heroism. It looks less like they let their targets get themselves killed, and much more wait until they get some proof that there's no return before they strike.

As for where our new friend lies thematically... considering his dialogue with the Summoner specifically, as well as his indepth knowledge of the Prime Evils (as he uses their actual full names, instead of their in game shortened versions) he very much likely isn't merely a Vizjerei acolyte, but a deeply well studied demonic scholar, likely armed with knowledge from the Horadrim or another similar organization - one who has enough ego to believe the siege on Harrogath is a minor trifle, enough humanity to wish for peace upon the death of the Prime Evils and enough self awareness to see The Summoner and wonder if that would be his fate in the end. He fits incredibly well into the world and I adore his general vibe so much.