No, I don't think that's the problem[1]. It's the unrealized gains, whether or not they take out loans. And I suspect (with no data) that by far, most unrealized gains have no loans against them.

[1] There are two versions of what "the problem" is. The first is that people can accumulate assets, completely untaxed, in the form of unrealized capital gains. The other problem is "we [Congress] don't have enough money". For either problem, VAT doesn't really address it.