I've done several jobs that have had old asbestos shingle siding and the right to do it is to just remove the asbestos shingles, and have a fresh even surface on which to apply your foam underlayment. If try to go over the brittle shingles, they will crack and fall apart anyway, and you will have a big mess behind your vinyl. As Jay noted, this will also allow you to know where the studs are, as I am guessing the sheathing is probably Homosote, which was popular as shingle underlayment, and it will not hold a nail. As far as screws for a siding job, that would be a royal pain, given the number of fasteners that must be used. Removing the asbestos tile is not hard with a flat bladed shovel, and since it is a rigid type of asbestos, is not considered highly friable, like the asbestos insulation on pipes that turns to powder when you remove it. I know, someone is going to respond about the inherent dangers of even touching asbestos, but the truth is, rigid asbestos shingles should not be considered dangerous unless you smash it to little pieces and make a a pile of dust. Wear a face mask or, better yet, a respirator, with an asbestos filtering charcoal canister and you will limit your exposure to any dusts that might be generated. Finding a landfill that will accept the labeled asbestos may be your most difficult part, but they're out there. Good Luck.