As far as going to the ohel there is no davening to the Rebbe ch”v. When one writes a Pan (or kvittel) the minhag is to start off with the words ??? ????? ????? ???? . We ask that the Rebbe should intercede on our behalf and be ????? ????? from Hashem that’s how every kvittel starts.
As for the permissibility of this the ???? ????? (who is not a lubatcher or biased according to some posts here) writes this is not only permissible it is a MITZVA. See ??? ???? ????? ???? ?? look it up for yourself please.