I think, given that there was, IIRC, mention of Soulfire pouring from the cracks in the ground in that conflict, it implies that the WG (or some Archangel) approves of Harry's use of Soulfire. Especially in that circumstance.
I don't think Soulfire is intrinsically linked to Harry's Starborn status, but in a mental struggle like that, I think it can help, for sure.