Is The One Ring rpg playable with a single player?
It should be; there is very little non-traditional about it. The most non-traditional element is the courage system.
The hope system, to some extent, is geared for 3-4 players. Since it has both individual and group dynamic elements, it may not be as good in a 1-on-1 game, but it should still work. The one element that is problematic is that one can always draw from the pool with group permission if one is the sole member of the group.
Also note: a larger group, in addition to having more hope in the Fellowship pool, has more diverse skills available, and thus is likely to need less hope spent in play.