Is warning against the one whom has deviance in his Minhaj considered that which will draw one closer to Allah?
Yes! This is giving sincere advice, this is from giving Naseehah. Thus, if yousee that a person has a deviation in his Minhaj, it is upon you to first advise him and clearly explain to him that which is correct while warning him from the deviant methodology. If he does not accept it, then warn the people around him to get far away from him.
However, in this affair there must be restraint. This is because some people think that (every single mistake) is a deviation in Minhaj. Therefore, it must be known what exactly this deviation is from the Minhaj and not just conjecture from the one who questions that this is a deviation when it is not in fact a deviation. Rather, I say, if it is confirmed that it is a deviation; then at that time give this individual advice. If he recants and returns to the correct Minhaj -Al hamdullah-; if he does not, then make it clear to the people that he is not on the correct methodology so that they will avoid him.
Accusations are not constructive and are of no benefit. Accusations, lying about people and accusing the innocent is not permissible. You must confirm (the facts) with a firm confirmation which is neither doubt nor error that this is in fact a deviation in Minhaj. Not everyone who says this is a deviation and that is not the right methodology is correct.
Presently, there is a very evil phenomenon amongst the youth. Each of them is warning against the other, even to the point that their blameful (behavior) has been extended towards the Scholars and they (these overzealous youth) warn against the Scholars. This is from the Shaytaan; this animosity is from the Shaytaan.
The Facts must be confirmed. It must be known that this is a deviation and defined. The person must be gone to (and advised) so that perhaps he will repent and leave off this deviation. If it is confirmed that they have deviated and they remain upon that deviation; then warn against them.
As far as mere accusations (no), the origin is that a Muslim is trustworthy, this is the origin, especially the Scholars. The origin amongst the Scholars is trustworthiness and good. A persons unsupported speculations will never be enough, nor hearsay which is built upon, no, this is not permissible. These affairs must be confirmed. The Muslims are brothers. You must spread love, co-operation and the giving of good sincere advice between them. It is not permissible to spread between them hatred, enmity and discord due to affairs which are insignificant, speculative and/or based on lies. Nor small issues which are thought to be big, none of this is permissible. The issues must be confirmed and Allah The Most High knows best.