Fallacies and Validity

This post is based on a Debate.org challenge. The question is can a statement based on an informal fallacy be true? The answer I give is it matters how you look at it. For instance, if Jim says what is going on in Ferguson county is appalling--the cops have been given a raw deal--you could say, "I know Jim to be a racist and therefore does not know what he is talking about." This is an ad-hominen attack. There are two ways to look at this--his racism is important in this context, since it is about race, or it is not since it is not about Jim. The first way suggests an informal fallacy can be valid since Jim being a racist might color his worldview. On the other hand, if one says this is not valid, they are saying Jim's being a racist does not matter and you should only listen to his argument. Oddly, the notion of informal fallacies, as opposed to formal ones, suggest such an argument is not valid, but this just doesn't feel right. Of course Jim's racism is important in this situation. My argument is this, Jim's racism does not lead to a valid argument, but can be an important factor nonetheless. It should be weighed as evidence, but cannot be used alone for determining correctness. Extrapolating this we get, no informal fallacy can be used, on its own, to determine the correctness of an argument and in a vacuum of other information cannot be valid. Just because Jim is a racist at other times does not mean he will be this time, but it offers evidence that he might.