I don't think you can become a Feruchemical Savant, but he may well have been a Gold Allomantic Savant. With that said, I'm not sure how compounding would effect become a Savant. If Chaos' theory is correct and I would guess that it is indeed, then the prolonged effects of the investiture on your body are what change your Spirit Web and make you a Savant. While Miles was burning gold a lot, he was then compounding the investiture into his Metalmind. I suspect that this would stop the changes to his Spirit Web.