Zuko wouldn't be able to hunt with the Xojan. They require at least a year of training alongside them, and they wouldn't trust Foreigners to stick around long enough to complete that process. However, there's nothing stopping him from trying to hunt Rakenga on his own or with other Foreigners! The Xojan would be a bit miffed if they find out, but grudgingly impressed if Zuko's successful - and as long as any Rakenga brought down are used as a food source in Hatal (i.e. not kept by the Foreigners for whatever reason), no one will object.