Yes it is totally safe to soak the board in alcohol so long as it is not energized. Be sure to air dry it or use a blow dryer on it to evaporate the alcohol before plugging it back in. Alcohol will not however do much to the corrosion itself but you probably should use a brush to loosen any corrosion while it is submerged. Do NOT use water at all, at anytime or the unit will not dry out very good and the corrosion will grow!
You could also use a pencil eraser to remove the corrosion.
Good luck, I hope this helps.