The reason I suggest using pure lemon oil on Ebony fingerboards is because the heavy turpines in lemon oil and in the Ebony are similar. The water and smaller molecules evaporate out of the wood rather quickly, but the big turpines take longer, and they are more destructive when they do since they are big. When you condition the board with lemon oil, you stuff some of those broken cells with chunky lemon turpines, and that protects the layers below it.
There's nothing wrong with pure mineral oil, or any other oil you like to use. On one account, you're cleaning debris off with it, and just about anything will do for this purpose. The lemon oil provides cleaning and conditioning. But if you're taking care of your fingerboard with any suitable substance with any regularity you're way ahead of most.