The Ring of Saruman?

[Raynor]

Do Sam, Frodo, Merry, Pippin know who Illuvatar/Eru is?

In letter #297, Tolkien states that:

We are in a time when the One God, Eru, is known to exist by the wise, but is not approachable save by or through the Valar, though He is still remembered in (unspoken) prayer by those of Numenorean descent.

In the light of this, I doubt any hobbit knew of Eru.