Do Ribbons have other effects besides for Contests

Bulbapedia has an extensive article on it, but it boils down to, in Generation III and on, there is no difference in stats between normal Pokemon and shiny ones.

Generation II (Gold, Silver, and Crystal) is the exception because shininess is determined based on the stats of the Pokemon. Namely:

If a Pokémon's Speed, Defense, and Special IVs are 10, and its Attack IV is 2, 3, 6, 7, 10, 11, 14 or 15, it will be Shiny

But, from Generation III and onward, it is determined based on a secret ID and a trainer ID, so it has nothing at all to do with the stats and will be just like every other Pokemon.

Something fun to note is that if the Male/Female ratio is 7:1, in Generation II, you cannot have a female shiny Pokemon because of the way it is calculated.

While an event Pokémon technically could come with EVs, I don't think any ever have.

Since you specified level 100, it sounds like you're concerned about them not being able to gain any EVs. If my hunch is correct, you don't need to worry about that in Gen V (their effort values are applied independently from experience). For older gens, you can check out the Box Trick (and read that anyway if you're interested; there's a note at the bottom about how it works in Gen V).