maybe I'm just too blind to see, but I've found no way to add an optional channel via the web interface of SUMA 2.1.
What I then did on the CLI was
suma:~ # mgr-sync list channels
[ ] SLE11-Public-Cloud-Module for x86_64 SUSE Linux Enterprise Server 11 SP3 x86_64 [sle11-public-cloud-module-x86_64]
suma:~ # mgr-sync add channel sle11-public-cloud-module-x86_64
Adding 'sle11-public-cloud-module-x86_64' channel
Scheduling reposync for 'sle11-public-cloud-module-x86_64' channel
suma:~ # mgr-sync refresh --refresh-channels
but I've yet to find the place in the web UI where I could do this. I couldn't even see the channel in http://suma.company.com/rhn/admin/setup/SUSEProducts.do - except that it's listed as "optional channel" in "SUSE Linux Enterprise Server 11 SP3" channel list. Which would not let me do anything to it.
I do see the channel and it's packages (after the CLI "mgr-sync refresh") in https://suma.company.com/rhn/software/channels/All.do - but do I really need the manual (CLI) steps to get there?