As I said, it's situational. Depends on the troupe as a whole, and more information is certainly needed to make this well informed decision. If Blackthorn is a House covenant of Tremere, I wouldn't have Talia target them.
Answering your point about this being a tie in to another saga, that's up to Peregrine_Bjornaer to decide. If he wants direct tie-in, I can say it hasn't been discussed (so it's not too likely) or if he wants the world to be slightly diffferent with similar covenants and personalities, but the events are different. He's indicated that he pulled covenants and characters from other sagas, elsewhere. However, I don't expect him to have the same reasons for the giants being aroused that I do. I don't expect him to have elements of House Guernicus attempting to destabalize and take over the Order. He's the SG.
This saga is basically picking up where this story left off. Duncan as apprentice and diabolist was a plot device to bring closure for Fiona (Peregrine's character), it was a story to let her see that she couldn't go home again, but that the home she was at wasn't as bad as she had thought. Peregrine's given me the highest compliment I could ever receive from a writer: being inspirational to an excellent writer.