Oh I meant like 3rd person-interaction between any of the traitor Legions, like we saw the interaction between a couple of Word Bearers in Vulkan Lives, or are they all unnamed unknown faceless protagonists?
There's a Word Bearers end-of-level boss, a Word Bearers mid-level boss, and a Death Guard final boss. They variously talk to each at certain points. Don't get your hopes up if you like traitor/traitor interaction beyond 'baha i will betray you' 'not if I betray you first'.
I don't know if we're doing spoilers, so I'll just say there is another marine from a traitor legion in the book, and his plot is at least interesting, if kind of dumb and seemingly pointless.