I don't think it is a SPAN issue, as VIX options are not futures options, although they may be "priced" off of where the futures are trading vs the underlying options.Yeah, I was surprised, too. and I called them and they confirmed that so far they just don't like the risk profile of the product, although it may be an exchange issue or some clearing issue, or even SPAN, I suspect. I have portfolio margin, futures options permissions, SPAN (obviously), etc on that (mon-retirement account) account.
. Here's spec from CBOE: