Reb Nachman never said to come to his grave for Rosh Hashanah. If he would have do you not think that Reb Nathan would have written it down? He only said to come to his grave and say the ten Psalms. And he brought two witnesses to make sure that this could never be misunderstood. But he never did any such thing concerning Rosh Hashanah. He said to come to him on Rosh Hashanah when he was alive. He never said anything concerning his grave.
First let me make it clear that I did take a lot of time a effort to understand the opinion of Bava Sali concerning this issue. Clearly he had a very high opinion of Nachman. What he apparently did not like were the small groups of cults of people that use his ideas to make up a new Torah. But that did not diminish his respect for Rav Nachman himself. towards the end of his life he related a dream he had of his son coming to him from Gan Eden telling him how Nachman was telling a Torah lesson to the tzadikim [saints].
The minimum we can learn from this story is that Bava Sali did in fact have a positive opinion of Rav Nachman.
Reb Moshe [Feinstein] we also know did write a haskama [endorsement] on the petek of Israel Odesser.
Though this does not tell us anything about the petak [letter] again it is a clear piece of evidence that Reb Moshe also had a very good opinion of Rav Nachman.[especially if you see the actual word that Reb Moshe wrote.]
[And Rav Ovadia Joseph said it is allowed to come to Uman for Rosh Hashana. Rav Shach said no.]
What needs to be looked into here is the fact that some people do tie themselves with Nachman.
According to the Nefesh Hachaim that is idolatry My view of this is that one can do everything R. Nachman said and he or she should just be careful not to fall into idolatry.
I think that Rav Nachman came to help people keep Torah.
However there is a opinion that seems to be a basic belief in Breslov that one cant get close to God without going through Rav Nachman. This would be easy to dismiss if it was just Breslov. But they bring it from a statement of Rav Nachman himself in the Chayee Moharan. however if you look there at the actual Yiddish statement that Rav Nachman said you will see he said no such thing. Rather this: "There is something that comes into the world, that when it has come one can't get close to God without it." He did not say it was a tzadik or even a physical thing. Perhaps he meant it is some kind of spiritual dimension? see the Yiddish right on the page and you will see what I mean.