SUSE Manager can sync channels from NCC through a corporate proxy.
Channel syncing is done with mgr-ncc-sync. It supports both http/https protocols as well as authentication for proxies.
The easiest way to configure the proxy is by using yast2. mgr-ncc-sync will then read the proxy configuration from yast2's config files. Alternatively, the environment variables HTTP_PROXY and HTTPS_PROXY can be set.