After the fact you are able to try and prove that the money or assets were not used in the commission of a crime. How one could ever prove a negative is beyond me, and the burden of proof is higher than that required by the constitution which (IIRC) take the innocent until proven guilty perspective.
These poker sites have not been convicted of anything, nor was there a court proceeding where the siezure was proposed and the owners of the property had an option to defend their rights.
Further, as we've seen in case after case, even in situations where the victims are not involved in crime at all, the courts are stacked against them.