Yes as a Warlock you can raid with your Felguard In Karazhan there are times when you don't need him or you do.I manage to down a few boss with or without my Felguard and learn to adapt to using him in when I realize he was useful to finish off Bosses who are down 5 to 2% of there life.

It doesn't matter if DPS is crapy but you can still down a Boss if you listen to your Raid leader or Raid Warrings mods that tell you, and like the saying goes by someone "Its easy as taping two buttons." I manage to down Nightbane when he had 6% health and seen how my Felguard manage to do what damage and help down it. Prince Malchezaar he was Hard as long as you Soul Link with your pet you can live through it.

The Curator yes your Felguard would come in Handy when people need help with the Adds he summons who do damage Its best to have him Fight off the adds while you drain life.Shade of Aran that guy was hard to do but I didn't need my Felguard for him I used my Felhound because he adds reistance plus Buffs I manage to live through that one.These are just examples of course learning to use a Felguard it comes in handy whne your in area's of Karazhan you do need him or you don't.