I've seen alfgar shouting in his usual spot in ul'dah when he does as far as i know the imperials are always just north of camp horizon, i've also seen a npc begginning with r in camp tranquil shouting about the imperials but i havent seen where they show up in the black shroud. To get a taste of victory you need to talk to the npc near the group of imperials to join the fight against them and then keep fighting them untill they retreat and open a chest containing deaspected crystals. You dont get any sp from killing the imperials as far as i've seen but you get quite a few shards.