While playing the Hex campaign, I noticed that the PvE packs contained two commons from PvP sets and one PvE exclusive card (also two slots for equipment or stardust). Are those commons from a set pool, or can they be anything?
The commons are from a limited pool, so you won't be able to get all PVP commons that way. From the website
packs will always contain five total reward items, which will consist of some combination of equipment, PvE cards, Stardust, and a subset of PvP commons
Of course you can always pick up commons from the Auction House using the gold you earn in the campaign.