Ugh, skill swap chains. Anyhow, just tested it with normalize skitty relayed to skill swap reuniclus relayed to a volcarona with will-o-wisp, against a wild drifblim in double grass. It burned drifblim, yes. And to be sure I did it right, I used bug buzz from the same volcarona on drifblim the turn after, where it gave the "It didn't affect Drifblim" message. So yeah, will-o-wisp is akin to, say, hypnosis on dark types, where the typing of the move in itself makes no difference on what it can and cannot affect.