Yes. Also, all sources of experience points are applicable. The best way to level abilities is to put them on your secondary weapon bar and switch to that while turning in quests. Since your main issue seems to be leveling that specific ability, it does not matter how many shadow abilities you have on your bar, each individual ability will only gain the experience once and only as long as it is on the currently active action bar.So if I only have shadow line skills slotted, all the Xp will go to that skill line?