DoW has a Lore cards FAQ up, and their answer for this is "capped at 1".
Additional Subsequent Lore Card Effects? (Comment / Question)
Question: On my next turn, while my unit(s) are still shadow-walked, may I play a Lore card such as Strength to enhance my shadow-walking units attack dice by +1? Or is a shadow-walked unit capped at 1d and unaffected by ANY subsequent Lore card effects while shadow-walked?
Answer: a shadow-walked unit is capped at 1d and unaffected by subsequent Lore cards while shadow-walked.
I would assume the same applies to cards that would affect how many dice are rolled against it, as well.