I agree with @Pallas4 that if the Cadmus player decides to treat the parasited enemy as friendly then that model may also choose to suffer damage.
Parasitic Grasp says:
"During friendly Activations, Cadmus models in this Crew may treat enemy models with a Parasite as though they were friendly Cadmus models (except for Schemes and Strategies)."
And Siphon Power says:
"After this model declares an Action, a friendly model with 4 may suffer 1 irreducible damage."
So rules as written I would say Pallas is correct and in theory it might score Hidden Martyrs. The point of discussion is whether this would then also count as "..killed by an enemy-controlled model". As the model taking the damage is choosing to die, even though the Ability is on an enemy controlled model, I doubt that killing itself counts as being killed by that model. But that is definitively a point for discussion.