Not a problem IF AND ONLY IF, the surrogate father KNOWS that he is not the dad when he assumes the parental role. However, if the mother LIES and through FRAUD represents the child as his when it is not, then the surrogate father has been duped and should have legal recourse.
No. I think if the child comes to know the man as the father - even if he is not - he should still be responsible for maintaining their personal relationship with the child, as well as providing financial support. The real dad should provide financial support, also, so each pays less than they would normally pay if they were the only financial provider.