Works like a charm. Get in a group and activate your combat log(take care to have all messages activated in you c-log). This feat increases the dmg output of the whole party (not just yours) immensly, especially, if you have Necros that are specced for pets.
It depends on your style of attack. If you are only white swinging (not reccomended) you'll see Fiery proc by itself as its own line. If you only use combos, it gets added into the combo line if it procs for a combo.
1000 hit with a 600 Fiery proc looks different like this.
1000 Slasing damage to ???
Fiery Weapons hit ??? for 600
Hellstrikes VI slashes ??? for 1600
Its one of hte reasons many dont think it is working. Normally see it every 12-15 swings.