Utah: Peyote Case

In Utah, a couple started a religion that uses peyote as part of the ritual.  Arrested in 2000, in 2004, a unanimous Utah Supreme Court held that they were exempt from prosecution under federal law.  They now face federal charges.  Among the issues: Does the federal exemption have a racial test (the statute does, the reg does not) and for the mistake of law defense can an individual reasonably rely on a state supreme court's interpretation of federal law?  [Jack Chin]