One of the Devs would probably answer this better.. But i will give it my best shot.
I think it's Part of the main game.. Why? He got sent to the Kessel space mines because of Jabba .. Because jabba thought he became too big.. and Could pose a threat. However Tyber knew things about the imperials ( Contacs , and Personal experience) So i think the Holocron will probably function as a Power Up device for the Eclipse ( This is highly Suspected )