No, they won't corrode a steel bike. As others pointed out, aluminum doesn't grip into steel frames well and with more horizontal dropouts can slip under heavy load like an out of the saddle climb. During a cross race last fall I ripped the back wheel out of place so the tire would rub the non-drive side chain stay 3 times on the same short off camber climb. Not the fastest rider due to my weight but plenty of power and it sucked having to stop, try to under the skewer and reset the wheel. Vertical dropouts have no trouble with this at all.