The VS Battles tiering sytem works differently. We do not believe omnipotence = tier 0, or any tier for that matter.
That was Mandrakk's personal interpretation, which he is by all means entitled to, but is assuredly not the site's stance on omnipotence. This article would be a better explanation of the site's stance.
Basically, the term "omnipotence" is paradoxical term. In it's literal definition, it implies "all power", which can simply be inferred as unlimited power. The alternate interpretation is to have "almighty power" or "unlimited power".
However, the alternative interpretation of omnipotence implies inherent superiority over everything, transcending even logic and conceptualization. As such, it cannot logically be part of an heirarchical structure, since omnipotence > all, including omnipotence (makes no sense whatsoever, I know, but logic is superceded by omnipotence).
Any character cannot be listed "omnipotent", since the base premise itself is a paradox which cannot exist. True omnipotence (not the "omnipotence" flung around way too often in fiction) is impossible to define, and is too contradictory to make any sense. It is best utilized in religious or theosophical literature and research, and it certainly has no place in fiction.
To that end, VS Battles steers clear of omnipotence, since the entire issue is, crudely put, a complete and absolute waste of time and mental energy. The community neither denies nor acknowledges "omnipotence" when listing a character.
Eru is the supreme being of the TolkienVerse, but as per our tiering system, that alone does not merit a Tier 0 rating.
@The Omnipotent One: That is an old argument, and has been done before too many times. I could type out a paragraph for that too, but I think I've already said way too much.
Suffice to say, beings in fiction are considered equivalent to real-life beings, and fictional realms are considered to be equivalent to our own, all considered to be a part of the omniverse.