Iran entered Syria , overall in minor capacity with deploying more or less significant military presence only in Damascus and Aleppo. Prior to russian intervention Nusra was in Ghmam latakian village , being able to shell Latakia from there. In regard of sectarianism, this is partially sectarian conflict indeed, buth not a true reason for the syrian conflict
There are no way sunni extermists in whatever county are going to change theirs sentiment toward Iran. So, I dont see a reason for concern related, what they thing of any iranian action in particular. Iranian reluctance to aid Assad more actively led to an almost regime colapse in autumn- summer of 2015