The majority of Blokes playing in the NRC would have played either Super Rugby, Club Rugby, or both within Australia this season. There are a few exceptions, off the top of my head, Steve Mafi (Australian born Tonga international Lock/Blindside, signed for the Force in 2015), Cameron Treloar (Aussie Lock played in France for the last decade, swan song for NSW Country) and a couple of Pasifika boys signed for 1 or 2 NSW sides.
Most of these blokes would be Australian eligible. Of the rest, they're split into Blokes who could be eligible to play for Aus after residency (e.g. Telusa Veainu and Sefanaia Naivalu of the Rising), or players who've been internationally capped by a Pacific Nation, either at Full level or Sevens.
The experience that the other 29 blokes on the field would get playing with a full professional like Steve Mafi would be a bit more important than the 80 minutes into a Lock who could simply be journeyman player.