Q. Can a Cohen visit Kever Rachel? Can a Cohen enter the burial cave of the Sanhedrin?
A. (See question 2274). There is a tradition ascribed to Rabbi Yitzchak Alafia, that Kever Rochel was built in such a way that it is permissible for Cohanim to enter. (Ahavas Hashem p. 128, See also Divros Eliahu 35, Tzitz Eliezer 16: 18, and others that are lenient).
However, Zais Raanan (2: 26) quotes Horav Shmuel Salant's zt'l ruling that it is Biblicaly prohibited for a Cohen to enter Kever Rochel.
Avnei Yashfa (Y.D. 3: 101: 2) permits Cohanim to touch the outside walls of Kever Rochel.
Nitei Gavriel (Avelus 91: 2: n. 4) writes that in practice the majority of Gedolei Yisrael, including R.S.Z Auerbach, R.M. Feinstein and the Rebbes of Belz, Satmar and Lubabitch zt'l, prohibited Cohanim from entering all ancient kevarim of Tzadikim including the kevarim of Meron.
Horav Shlomo Miller's Shlit'a opinion is similar also in regard to the kever of the Sanhedrin.
Rabbi A. Bartfeld as revised by Horav Shlomo Miller Shlit'a