Praise be to Allaah.
If the one who performs the nikaah is given something from the Bayt al-maal (treasury of the Muslim state), then it is not permissible for him to take anything from those for whom he does the nikaah. But if he does this voluntarily, and he is given something without asking for it, there is nothing wrong with that. If he is given something because he asks for it, I do not like that. Whoever wants to be independent, Allaah will make him independent.