The only time an award will affect the sibling's financial aid is when that school calls and gets the exact information from that college. These days, some schools are doing just that. However, if the award is a one time award that was given the previous year, I doubt it would show up when the the info is requested.
Friends of ours have two daughters at schools that give good aid packages. Yes, the schools do check that both girls are enrolled. They don't seem to be concerned about what the other school is getting in terms of aid, however, But that is just a small piece of the picture. THis is a changing scene, and with money getting shorter, I would not be surprised if some schools do get an exact accounting. It would be more fair to do so. But right now, most schools seem to be going by formula and just verify that there is indeed a sibling at a college.