I figure Merii got treated relatively well since her power is on the more conscious side. Can't really hook a car battery to her and put down some buckets to collect magic healing goop, gotta get her to actually cooperate.
And considering how Zeke seems to have been treated quite well, even though you probably could just strap him down and jab some needles in him to get the poison, the researchers probably lean more toward carrot than stick. It is a bit ambiguous though, and could just be a consequence of him appearing to be quite calm and passive.