To answer the OP's original question, no, Bhelen is not the "Satanist" choice, because the idea presented by the satanist author isn't unique to satanism. The idea that evil serves as a catalyst by which greater good or progress is accomplished is a snazzed up version of the question do the ends justify the means. And that's been argued since the beginning of mankind. And that's assuming that Behlen even IS evil, which is also questionable. Bhelen and Harrowmont are not "good" and "evil" people. They are, instead, complex and multi-dimensional people. I stole a candybar once when I was young. I also used to volunteer as a tutor for intellectually challenged students. You can't site me as evil because of the candybar or good because of the kids. Maybe as people we do more good than evil, or more evil than good, but you can't just take one action and define a person by it.
Incidentally, the polarization of plot choices into the "good path vs the evil path" misses a huge point that the game makers were trying to make. In any given choice, there is reason to think either path is the better choice. For instance, take andraste's ashes. Everyone says it seems obvious that it's "bad" to destroy a healing religious relic. But there are reasons one might consider it not only not bad, but morally superior. For instance, let's assume the character you play does not believe in the chant, and believes that religion is ultimately bad for humanity. Beyond this, he is aware (because he luckily took Oghren) that the ashes certainly have restorative power because of the high levels of natural lyrium in the room with the urn. To this character, leaving the ashes alone will only allow the the further justification of what he sees as an unjust religion. At the same time, not being religious, by destroying the ashes he destroys nothing of value because he never believed it was a "sacred" relic anyway, and the further justification of religion by the ashes would end up killing more people than the ashes could possibly save.
For that matter, the character could be non religious and think destroying the ashes is bad for the simple matter that they can cure people, and having neutral feelings towards the justness of the religion they represent would happily let people believe what is false for the practical purpose of saving more lives.
So, the idea that Bhelen is pure evil is questionable, and even if one could demonstrate the total sum of his actions justified that label, the question of whether this evil serving as a catalyst for good is not a question of Satanism, or any religion, but instead a question of moral philosophy. And as to the answer to the question of the ends justifying the means, at this point in human history, the correct answer is not really a known one.