I've set the system proxy up to use our proxy and to do so without a login; if I set Firefox to "use system proxy", I can get out to anywhere on novell.com fine.
Thus I know the proxy is working.

Let me repeat that.. or just read it again. The proxy is working. I can get to nu.novell.com via a browser, using the system (not separate browser) proxy settings, with no login required.

But I can't (re)register or check repositories, or do updates.
(At one time the server had a public IP and didn't need a proxy, so it has a repository that I can't get to now)

suse_register -a email=<my email> -a regcode-sles=53A22B0743A934 -L /root/.suse_register.log

Returns

Refreshing service 'nu_novell_com'.
Repository 'SUSE-Linux-Enterprise-Server-11-SP2 11.2.2-1.234' is up to date.
Abort, retry, ignore? [a/r/i/?] (a): a
Abort, retry, ignore? [a/r/i/?] (a): a
Abort, retry, ignore? [a/r/i/?] (a): a
Abort, retry, ignore? [a/r/i/?] (a): a
Abort, retry, ignore? [a/r/i/?] (a): a
Abort, retry, ignore? [a/r/i/?] (a): a
Problem retrieving the repository index file for service 'nu_novell_com':
Download (curl) error for 'https://nu.novell.com/repo/repoindex.xml?cookies=0&credentials=NCCcredentials ':
Error code: Connection failed
Error message: Couldn't resolve host 'nu.novell.com'

Check if the URI is valid and accessible.
Skipping service 'nu_novell_com' because of the above error.
Some of the services have not been refreshed because of an error.
Download (curl) error for 'https://nu.novell.com/repo/$RCE/SLES11-SP2-Core/sle-11-x86_64/repodata/repomd.xml?credentials=NCCcredentials':
Error code: Connection failed
Error message: Couldn't resolve host 'nu.novell.com'

Problem retrieving files from 'SLES11-SP2-Core'.
Download (curl) error for 'https://nu.novell.com/repo/$RCE/SLES11-SP2-Core/sle-11-x86_64/repodata/repomd.xml?credentials=NCCcredentials':
Error code: Connection failed
Error message: Couldn't resolve host 'nu.novell.com'

Please see the above error message for a hint.
Skipping repository 'SLES11-SP2-Core' because of the above error.
Download (curl) error for 'https://nu.novell.com/repo/$RCE/SLES11-SP2-Extension-Store/sle-11-x86_64/repodata/repomd.xml?credentials=NCCcredentials':
Error code: Connection failed
Error message: Couldn't resolve host 'nu.novell.com'

Problem retrieving files from 'SLES11-SP2-Extension-Store'.
Download (curl) error for 'https://nu.novell.com/repo/$RCE/SLES11-SP2-Extension-Store/sle-11-x86_64/repodata/repomd.xml?credentials=NCCcredentials':
Error code: Connection failed
Error message: Couldn't resolve host 'nu.novell.com'

I get the same sort of thing trying to use zypper to do a refresh.
It resolves nu.novell.com using the browser with system proxy settings.
So.. it seems that curl/zypper/whatever is ignoring the proxy.

zypper does the same:

varan-new-vm:/etc/zypp # zypper sl
# | Alias | Name | Enabled | Refresh | Type
--+--------------------------------------------------+--------------------------------------------------+---------+---------+------
1 | nu_novell_com | nu_novell_com | Yes | Yes | ris
2 | SUSE-Linux-Enterprise-Server-11-SP2 11.2.2-1.234 | SUSE-Linux-Enterprise-Server-11-SP2 11.2.2-1.234 | No | Yes | yast2
3 | SUSE-Linux-Enterprise-Server-11-SP2_11.2.2-1.234 | SUSE-Linux-Enterprise-Server-11-SP2 11.2.2-1.234 | Yes | No | yast2
varan-new-vm:/etc/zypp # zypper lp
Refreshing service 'nu_novell_com'.
Problem retrieving the repository index file for service 'nu_novell_com':
Download (curl) error for 'https://nu.novell.com/repo/repoindex.xml?cookies=0&credentials=NCCcredentials ':
Error code: Connection failed
Error message: Couldn't resolve host 'nu.novell.com'

Check if the URI is valid and accessible.

I'm a loss at this point.