Well they have some oversight of foreign accounts for tax evasion purposes but that is out of my wheelhouse and I am not up on those. But so long as there is even the suspicion of the use for tax evasion they will investigate and regulate. You only need to remember that Al Capone was arrested for tax fraud/evasion not all his other misdeeds. There are other possible twists. When automatic weapons were restricted they did it through taxation. It was illegal to own one, but if you owned one you have to have a tax stamp ($650 as I remember) on a permit. If you registered it they arrested you for having an illegal weapon. If not then you could additionally be arrested for tax evasion when they found one. Where there is a will there is a way to tax it.