Well, he said in the interview that he crafted them with the intention that they would be, specifically they should be suitable for all of the work in Nine Doors of Midgard, which he has completed (along with being a master in the Thorsson-founded Rune Gild).

I suppose your confidence in that claim would come down to how much you believe the Runes' efficacy as a divinatory medium is due to their divinely-revealed nature, and how much is due to being a handy set of symbols that we can graft meaning onto, and how much confidence you have that that he is qualified in one or both of those approaches.