Are you sure that is metal and not actually the leather saddle strings going all the way through the sheepskin?
Good saddles used to be made (and some probably still are) with the strings running all the way through the tree and through the leather skirts. The strings actually held the skirts on instead of all the screws, nails and tacks people use now days. (Skirts are your bottom most layer with the sheepskin). If the strings ever broke, it would not be uncommon for someone to redo the saddle strings and have the strings on the outside of the sheepskin.....because it would be very difficult to get them inbetween the sheepskin and leather on a saddle that is already put together. I had a saddle like that once. The sheepskin was thick enough to make up for the lump of the saddle string.
I agree with Southern Trails, with a pad the horse should not even feel it. If they do, which is always possible I suppose, I would be really surprised. I would try it out on a good long ride with a good pad and see how it does. If you don't have unusual spots or pressure points on your horse (like raised spots or spots without sweat) you are good to go. But make sure the horse is good and sweaty first, because otherwise you might have dry spots from not enough sweat rather than a saddle issue and you will worry yourself for nothing.