is there any serious heter to allow a male photographer to take pictures and to fim the women dancing at a wedding or would it be an isour of lifnei iver for the baal simcho?
As a side point, once you are asking if it is lifnei iver for the baal simcho, it would also be lifnei iver for the women dancing at the wedding, as they should not dance in front of a man.
Getting to the actual question; it is better to have a woman photographer for the women, and there are people that specifically want this. In fact there are some poskim say that it is actually assur. On the other hand there are poskim that say that it is permitted, since the photographer is busy concentrating on the job that he has to do and not on the women in the picture. Many people rely on this, and don’t specifically get a woman photographer for the women.
Anvei Derech 9-158, Ohel Yackov -Yichud pg. 183 brings from Ohr Yitzchok 2-10 and R’ E. Auerbach shlit”a that it is assur, Shut Olas Yitzchos 2-253. Malbusei Mordechai 12-7 in the name of R’ Vozner zt”l and Ohel Yackov ibid in the name of R’ Eiyashev zt”l, also Om Ani Choma –Tzion Hamitzuyenes 322, that it is preferred (but not assur) to have a woman photographing the women. Olas Yitzchok 2-235 (2), Ta Shema – 8 pg. 150, say that it is permitted.