"Yeppers" is something most Americans would understand, but in reality few people say it.
Honestly, "Yeppers" would only be said by people wanting to appear a bit ridiculous -- in other words, for humorous effect. The word is excessively cute. So I can imagine someone writing "Yeppers" as a funny way of saying "yes" on Facebook or via text message. But in real life? I can't remember anybody ever saying it seriously.
One example would be the American version of "The Office" (originally a British sitcom). The primary character is meant to be a bit of a buffoon. In one instance, he says "yeppers" for a laugh:
So Yeppers.com has a cutesy, weird tone. That would be its appeal. But "yeppers" is not a slang term that's much used except for self-satire.