There is no objective and honest way to answer this question. There is simply no way to tell how much, if at all, Congress has been swayed by lobbying and campaign contributions. Two things to consider:
If a member of Congress accepts contributions from pro-ethanol sources, it might be because he or she already supports ethanol. There is no way to prove a causal link between contributions and policy.
There are reasons other than economic reasons for backing ethanol. A member of Congress may vote to increase ethanol requirements not because they want to give “pork” to farmers but because they think ethanol is a good way to increase America’s energy independence.
For these reasons, we can never know why members of Congress vote as they do on ethanol. We cannot know how much they are influenced by lobbying or campaign contributions.