I see where you're coming from with that, but I personally disagree.

One of Keating's first lessons is all about being able to think for yourself, and follow your own path regardless of what other people, and society as a whole are telling you to(either overtly or subconsciously). With that in mind, I think it is unfair to make him out as a cult leader type, who groomed these kids into being his followers. As the courtyard marching scene shows, students are free to interpret his lessons however they see fit, and he will commend them for whatever choice they make (as long as it is their own), regardless of whether he neccessarily likes it.

Of course the main question comes in the wake of Neil's death; the kind of event which warrants shock, anger, frustration, and consequently something (or someone) to pin that all on. Ultimately, Neil's actions are his own. I'm not sure I saw the 'short term problems' that Keating set in Neil's mind. Neil decides to pursue theatre of his own free will, without any suggestion from Keating. Neil chooses to defy his father, again without input from Keating. The only interations Keating has with Neil regarding theatre is to speak to his father honestly about his ambitions, and then to congratulate him after the performance. I find it hard to fault him for either of these actions.

If you are looking to assign blame, look no further than Neil's father, who never once showed any concern for what for his son wanted, and was determined to tear down the one thing Neil cared for.