I'm not familiar with Ursery and have only skimmed a few sources, but I saw nothing suggesting that the legality of civil forfeiture per se was even disputed in that case. If I read Stevens's dissent correctly, it challenges only the constitutionality of one of the involved criminal cases, arguing that because the previously seized property did not represent proceeds of a crime, the perpetrator had a legitimate property right of which the government had deprived him. Therefore, the forfeiture already served as a punishment for the crime, so double jeopardy precludes a subsequent criminal trial on the same offense.

I'd be interested in knowing if I'm missing something important here.