I really see no reason why Nole can't beat Rafa at RG. I can almost see more reasons for why Rafa can't beat Nole.
Peak Nole owns Rafa on every surface just like peak Rafa owns Roger on every surface and peak Roger owns Nole on every surface.
Yeah, playing at RG is a mental advantage for Rafa. But before this year you could say Rafa owns Monte Carlo. And what happened? Nole beat Rafa at MC final. The same can happen at RG too. Nole isn't afraid of Rafa.
Of course, RG is Bo5, M1000s are Bo3. But I don't see that as an advantage for Rafa, Nole has the fitness Bo5 requires, I'd be more worried about Rafa's fitness after his seven-month break. If Nole does better than Rafa in Rome, then he's the obvious favourite.