Our cloud solution at the moment does not allow for L2/L3 ACLs or whitelisting to limit access to users. This will be implemented later in 2018, it's in the roadmap. However, if you enable guest access through guest access to through guest self-sign in, you will be able to see the guest in the clients section and have the option to disable guest or block guest. Disabling the guest user deletes the guest pass permanently and blocking the client and the client can be allowed back by enabling guest in this same section.
If you have further questions; will suggest to open a cloud account temporary account so that you can explore the option. There's a question icon in the upper right that will answer questions like the one you just posted by doing a search in the documention. You can always contact support Ruckus support at https://support.ruckuswireless.com