When Lashiec dies in PSIV, he clearly knows he is a servant of evil powers and expects to be revived in the future. Do you think he knew all of that back in PSI as well? There are a couple of conflicting backstories which suggest different things. In one he joins a religion in search of immortality - much like Zio. In another, he is slowly corrupted over time, sort of like the governor of Motavia.
So, did PSI Lashiec know he was serving Dark Force? Did he expect to be revived in his zombie form?