I respected Hissrad, even as I killed him. My Inquisitor felt it coming, but he considered Hissrad kadan anyway.
Hissrad did not betray the Inquisitor. He merely upheld his one and only loyalty, which was to the Qun. As Thom Rainier can say if he's in the party, Hissrad was honest with you from the start. I would expect Dorian to be loyal to his home country if a war ever broke out between Tevinter and the Inquisition.
The only problem I had with Hissrad in that moment was that for all his training as Ben-Hassrath, and all his experience with the Inquisition, he failed to see that Vidasala was wrong. All the evidence showed she was Tal-Vashoth, but even if she was working under official sanction and orders from Par Vollen, she was operating on pieces of information and she drew the wrong conclusion. Jerran knew it. That's why he helped the Inquisitor. Hissrad should have done the same. This is especially true knowing both the fact that the Inquisition had nothing to do with any plots formed by Fen'Harel, and the fact that the Inquisitor is not going to be killed by the likes of the Ben-Hassrath. He also should have known that as soon as Vidasala was stopped, the Qunari would disavow any knowledge or involvement in her actions, and would likely declare her Tal-Vashoth.
Hissrad's involvement should have come with two possibilities. If his approval was high, or if he was in a romance with the Inquisitor, then he should have simply refused Vidasala's order and then told her that he knew for a fact that the Inquisitor was not an enemy and had no involvement in anything related to Fen'Harel. That's one option. The other is if his approval is low, then he dislikes the Inquisition anyway, and doesn't mind seeing a dangerous thing removed from the world. These two options could also play into if the Inquisitor drank from the Well of Sorrows and used the correct phrase to greet the elven spirits. If he did, then it makes Hissrad think the Inquisitor is part of the elven plot. If not, and the spirits attack, then it proves the Inquisitor is not involved.
I also don't think the Chargers should have anything to do with his decision. Vidasala attempts to bring The Iron Bull back under the Qun, and to the best of my knowledge, he always refuses. Well, I think an Iron Bull with low approval of the Inquisitor should accept the offer. Basically, it should come down to whether he wants the Inquisition stopped or not.
I also thought there should have been an option to leave Hissrad alive, and capture him to be judged later. Same would go for the Chargers.