I don't think that's justified by the text.
Belegar never says it's likely to find runesmiths willing to come out and work far from the eyes of their guild. He says that being under Dwarven authority would make it easier to recruit runesmiths because the Cult of Thungni would breathe easier. I think the plain reading of this is "if the project isn't under dwarf authority, the Cult of Thungni might decide it's not worth the risk and none of their members get involved." The Runelord/Runesmith distinction you draw doesn't appear at all.
I mean for one thing who is going to argue with Kragg or Thorek if they decide to get involved due to personal connections? The Runelonds are not some kind of centralized institution, they are deeply idiosyncratic especially at the highest levels.