Manslaughter might be the charge, but it'd be a prosecutorial reach. Reckless endangerment with a grave indifference to human life is what happened here.
That's reckless homicide in CA and can be considered 2nd degree murder there if the wanton indifference, or gross negligence is willful or depraved. Notice their comments on the show. The act was the offering of the contest, which the defendants failed to consider any consequences in particular regarding the contestants, which is the important consideration. They only considered their own measly little assess, so they created the "waiver". In fact they refused to consider the consequences of their actions, either on their own, or when challenged, by at least one caller and then again when the woman got sick during the event.
I don't see 2nd degree murder as a stretch at all. The radio station is a business and they're required to consider and cover the particulars of what they're doing with due care, due notice of risk to the participants, and a cert of insurance for the event. Obviously there was no due care and in fact they simply admitted on the air that they didn't give a shit. They had waivers they said, and additionally indicated and implied with glee, that it was not there responsibility whatsoever. That makes the gross negligence willful and IMO depraved. I think a 2nd degree murder charge is appropriate and I think so would a jury of reasonable folks.