Aww,
השתטח על קברי הצדיקים ולהתפלל שם does not = pictures and does not mean he’s alive – all the R”N is saying is that his Guf has some kedusha via his connection to Hashem. Actually, Pictures as per Kaballah has Klipos and many Gadolie Baal Mekublim were makpid not to have their pictures taken (I recall a responsum in SHu”T Divrei Malkiel – who wasn’t even a Chasid – opposing it) I have no issue with the very pictures, but to take that the other way and worship it – THAT is an issue.
The concept of השתטח על קברי הצדיקים is already mentioned in Chazal more than once – nothing new here. (see Yavomos 122a in Rashi תלתא ריגלי in the name of Gaonim) No one has Taynes on the very Chassidus part – it is the extent how far nowadays Chabd has taken it to.
They have substituted the original i.e. a live or direct devekus to a dead one. Chassidus was meant as to have a live Rebbe (as the above Rambam) and not (as per R”N) ” להמצא השפע שם בצד מן הצדדים” The above R”N was not meant to take that as your primary source of Devekus Hashem.