The Exiles set (36 dungeon) will make it easier to progress to 45, and you can certainly use it until you get your 45 set. I know I did. It may not be the most time efficient however, attempting to get the full set. It's definitely not required.
At 45, I believe people either use the Moonwater Arena from faction token grinding (http://bns.endgame.p...lshield&stage=0
) or Poh (http://bns.endgame.p...lshield&stage=0
) which comes from Blackram Supply (4/6 Man) or E. Fleet Supply (24 man).