I just had a brainwave that told me that the inn is really the
Floating Log! It makes sense now!
Some have seen my twin at night, - Gollum,
floating on a log
treacherous as he be, - good master, let's feed you to Her
some said that he must be blind,
some said he could see. - I don't really know about this one.
I don't know him, never did; - Gollum never travelled to the Shire
he just bears my name, - floating on a log
as my twin, from Him he hid, - from Frodo
before he turned tame. - before he promised
I have those who shelter sought
served for many years, - being a peaceful hobbit inn
until treachery was brought
upon me from fears. - Sharkey's men etc
When He returned from His quest - Frodo comes home to see the Shire scoured
I've been long in chain, - there was a barrier blocking the road to the inn
foes at my door, - Ruffians
He can't rest - leaves to the West
Ainu is my bane. - Saruman
I=
The Floating Log
Twin=Gollum
He=Grodo
I didn't realize how close I was in my previous guess!
That was one great riddle,
Legate!