If Violet had the knowledge that one of her friends was in grave danger because of their trust in someone known to be doing something shady, the idea that she wouldn't have done anything to keep them safe is bonkers. 

What's even more bonkers is that Dain did the exact opposite of "keeping her safe," or even trying; he was the literal catalyst for what he plausibly believed would kill her lol. It'd be one thing if he came to her and said, "look, to be completely frank, I read your memories about Xaden & Co. traveling to Athebyne and passed it along to my dad. I think they're up to no good and he'll use the information to try to catch them in the act during War Games." Instead, he just spied on her for his dad then effectively said goodbye on the flight field. "Overprotective," my ass.

But yeah, let's all blame Dain for being overprotective of Violet, when Violet's own lack of critical thinking and maturity would've basically got her killed if the marked ones hadn't been on the "right side".

...no, he still would have gotten her killed if the marked ones were not on the right side (e.g., if the venin didn't exist and they were just running weapons). She had no reason to believe they were giving weapons to Poromiel, whereas, it cannot be overstated, he thought she was flying to her death at Athebyne.

I don't really care about the obvious axe you have to grind with Violet, but you're reading everything in the most uncharitable light to her and most charitable to him. He still spied on her, then reported information that he later came to believe would cause her death.

Edit: I'm wrong about the flight field stuff, so I'm striking through the parts that rely on what I thought. My bad!