I think they don't stay in touch in a family way, but I also didn't get the vibe when they did meet as part of the job that they hadn't seen each other in like ten years or anything. It is of course possible that if that happened rarely enough, he might not have seen it!
Yeah, I imagine that they'd have seen each other mainly in official contexts that would include minimal phone checking, so less opportunities to see it. Zhao Yunlan's reaction to it would definitely be interesting, in any case, and now I want the fic in which he sees it.

He killed a guy who had just stabbed somebody. That's not great law enforcement by my standards, but Ding Dun is a criminal who just assaulted and tried to kill the Lord Guardian and burned the Dijun register, and wasn't exactly standing down when Shen Wei arrived. There was an ongoing melée. That's not 'no basis as a tyrannical dictator' - he didn't randomly kill a Dixing pedestrian for standing in the wrong spot because he was bored or something.
The "tyrannical dictator" thing is mainly about him implicitly threatening the delinquents with violence. Ding Dun is more ... the Dixing judiciary is fucked up. (Then again, given how Ding Dun already escaped once with inside help, Shen Wei might not have a choice, unless he's willing to completely violate the treaty and ask Zhao Yunlan to set up a Dixingian-proof jail aboveground.)

I honestly never got much of a vibe that Zhao Yunlan is hung up on the "a DIXINGIAN killed his mother" part; for me that's always overshadowed by "my dad let it happen for the Greater Good and Professional Standards". But it's an interesting angle, I'll keep it in mind and check that scene again.
I doubt it's at the top of his mind, but I suspect it's there somewhere, albeit tangled up in the "my dad is an asshole towards people who are basically human and have been condemned to the darkness" feelings. More of a small extra button that Shen Wei's lack of tact could press.