I used the search function to look for mentions of Ranald in Knights of the Grail and all I got was that he is perenially popular with peasants and merchants, and is often viewed as more of a merchant god than a thief one (although merchants are viewed as thieves so not much difference to them). Peasant revolts are stamped down brutally but nothing is mentioned about systematic brutal execution of Ranaldites.
The action checking out Carcassone as a location for the project mentions that Ranald is proscribed, so that much is canon in DL. But what that actually comes out to (fines, flogging, exile, death, social pressure, overlooked so long as no one calls attention to it), we don't know. Mathilde got (lightly veiled) permission to be there, so long as she doesn't preach.
I think it shows that A) Ranald isn't well regarded by the upper ranks, including the damsels, and they want to keep him out, and B) that distaste isn't so heavy as to preclude interaction if the political realities would make it profitable.
Personally, I really, really,
really want the lady to be Ranald's daughter. Like, nearly as much as Cython romance. But the proscribed and "no preaching" thing indicates that he wouldn't have the pull to get Mathilde the trust of the Lady and her followers, so I really don't think she's one of his daughters. That makes me very sad, and I really hope there's some secret circumstances (ancient prophecy of doom if Ranald has a significant presence, or something) that means it makes sense for the Lady to be his daughter given what we know, but it's really unlikely.
But it wouldn't be the first crazy awsome thing to happen, so I won't give up hope quite yet.