Is one allowed to have marital relations on layl hoshana rabah?
The only nights when relations are forbidden, are Yom Kippur and Tisha Bav. The poskim mention some nights when according to the Zohar one should refrain, this includes the first night of Pesach, Shavuos, Rosh Hashana and SHmini Atzeres. The Misna Brura brings this practice, and Hoshana Rabab is not on his list. Even on the above days, if it is mikvah night it is permissible. In addition if one has not fulfilled Pru Urvu [boy and girl] some hold one should not be stringent in this matter. One who may come to hirhurim etc. should also not be stringent in this regard.
Mishna Brura 240:7 and Biur Halacha there.