AFAIK these people don't commit the crimes (the FBI doesn't want the violent acts to actually occur), they just are involved in planning them.
Can you entrap a vulnerable person into participating in a plot, by making them feel important or valuable or threatened or as if their problems will be solved, or by making them feel that they are otherwise going against the group social norms? I'd say: Definitely yes.
Consider that humans are generally easily, predictably persuadable:
* Many human trafficking victims are 'entrapped' by their pimps, unwilling to leave and persuaded that the pimps love them - it's not an anomaly but standard procedure for the pimps, who seek out vulnerable young women.
* In another field, there is research that a large number of confessions, even to serious crimes, are false. People somehow break down after hours of interrogation and confess to things that never happened.
* Soldiers in large numbers are trained to kill, and often for very bad causes (look at militaries around the world and throughout history).
* Look up Stanly Milgram's famous experiments where people were persuaded to torture others.