Haros:
IMO: If you are really close to either the bride or groom (the party you believe is being misled) then you should approach them directly. If you aren’t then you should approach a good friend or relative that is really close to that person, who WILL approach that person and inform him/her as such (and not use it maliciously).
As you said “if the other party knows about it and still accepts than that is fine, but i feel its my duty in case they don’t know to make sure they do the appropriate research.”
Definitely do not be anonymous. Anonymity is useless because people dismiss whatever is being said as heresy or rumors and won’t add any value to it.