Because of the 1980's anti-drug seizure laws; No, they dont.
Technically, the US government can 'subpoena' a wad of cash, or all your property. And because the Bill of Rights only applies to people, they keep the stuff. End of story.
Actually it's more like because the "Bill of Rights" is an inanimate piece of paper that has no bearing on the present-day government. In fact, it does more harm by letting people think that USG is bound by logical rules. Run through its amendments and see how many could possibly be considered effectual. I count three.
Technically, the US government can 'subpoena' a wad of cash, or all your property. And because the Bill of Rights only applies to people, they keep the stuff. End of story.