The Nevada caucuses are becoming a proxy for the racially tinged fight for the Democratic presidential nomination, with Barack Obama's campaign criticizing Hillary Rodham Clinton's allies for a lawsuit that could prevent some minorities from participating.On Friday, six Democrats and a teachers union connected to Clinton filed a lawsuit claiming the rules enabling Las Vegas Strip waitresses, dishwashers and bellhops to caucus inside nine resorts violate state law and federal equal protection guarantees. Other caucus-goers lack the same access, the suit argues.The Clinton campaign has said it's not involved in the lawsuit. The Obama campaign says it may not be …