A lack of a causal relationship wouldn't matter in that case. If something correlates with the outcome then it allows you to better predict the outcome even if it isn't the cause, because it at least correlates with the cause or it wouldn't correlate with the outcome.

Though obviously if it isn't the cause then you're better off taking into account the true cause rather than only the thing that correlates with it -- which would cause the correlation with the outcome to disappear for the non-causal factor when you take into account both.