For me the fact that he is able to consume it at all says something about it. We have no indication that he would be able to do something similar with say Allowmancy. Just being part of the the powers that stem from the shards of adolasium may not explain it. The question of inter changability was asked:
Question 2: Vasher has shown us that he can substitue his need for Breath with another investiture (presumably Stormlight). To what extent is investiture interchangeable between magic systems?
Answer from brandon on reddit 2. Very interchangeable, but not always simple to apply. So in a sense we are both correct.