I'm still not sure how I feel about them using elements from the EU and working them into the new canon because out of the context of their original stories it feels like it would be off to me. Plus I imagine it could be a bit confusing to anyone first coming into the franchise. It's not necessarily a bad thing and in some sense I like that they want to honor the EU history.
It can be done well or badly, like most things. In Marvel's main Star Wars title, in issue... 7, I think it was, a bunch of looted Jedi holocrons are brought to Luke and they all activate at once. Amid the babble, one of them is an exerpt of the Jedi who recorded that particular holocron saying in this one he will be talking about the Hundred Year Darkness. That is a reference to the Second Great Jedi Schism that ultimately led to the founding of the Sith Empire and, ultimately, the Great Sith War and all of the KOTOR stuff. But you don't need ot know that to get that it's a Jedi lore dump you're seeing in that panel. For less-read audience members, it's a throwaway that implies a backstory, a la "Years ago you served my father in the Clone Wars".
One area I feel they dropped the ball, though, is Thrawn in Rebels. In the original telling, the
Chimaera was one of the Star Destroyers at the Battle of Endor. Over the coruse of the battle, Pellaeon took command and, seeing the battle was lost for the Empire, withdrew. In the couple years that followed, his insistence on absolute adherence to Imperial Starfleet regulations kept the ship running well and not succumbing to the chaos nibbling away at the Empire. So, when Thrawn came back, he picked that ship to be his flagship. Now it was his ship before he went out to the Unknown Regions, Pellaeon was already its Captain, and -- in a needle-scratch across the record of Imperial uniformity -- the
Chimaera has a frikkin'
bas-relief chimæra on its ventral surface designed into the hull plating. Also not a fan of his voice (Thrawn, not Pellaeon).
And that's not even getting into areas where the makers of ancillary material -- or even more recent films -- have misinterpreted or misunderstood things from the OT or even the PT.