Is it permissible to act upon the fatwas and lessons of Sufi sheikhs despite their divergence in matters of shirk, such as seeking intercession through graves and righteous saints?

If the person whose fatwa is sought is engaged in an act of polytheism, such as supplicating to other than Allah, then it is impermissible to follow him or act upon his fatwa. This is because if he is aware of it, he is an evildoer (fasiq) from whom a fatwa should not be sought, as justice ('adalah) is a prerequisite for a mufti. If he is ignorant, then he should be taught, not asked for a fatwa. However, if he practices matters over which scholars differ, this does not prevent seeking his fatwa and acting upon his opinion.