Hello Hsu,
The current implementation for simple-gateways is only a partial implementation - hence the name 'simple-gateway'.
This was an unfortunate limitation mainly due to the fact that R80 was a management only release.
We are working on a full gateway API implementation (which will probably lose the prefix and become 'gateway' as in 'show gateway' etc).
In the meantime you have two options - the first is to use the 'show gateways-and-servers' command, which will show all the servers (including log servers, VS, clusters etc.), and filter the result.
However this will only allow you to view the objects not to modify them.
The second option in case you want to integrate gateway modification into a script is to the VSX Provisioning Tool which comes integrated with R80 (there is a section about it in the R80 VSX Admin Guide).
Hope that helps.
Yonatan
