We discovered Permanent Redirects (and probably Temporary Redirects) do not work if the Default Sites feature is enabled. It appears the Default Sites are defined in vhosts (in vhost_000_defaults.conf), so they must take priority over the global configuration that defines the redirection (in redirect.conf). They work fine if Defaults Sites is disabled.
This problem is resolved if I manually add the redirection domain to the ServerAlias of the vhost config, but it gets overriden if InterWorx rewrites the file.