OT: is there a way to have an Apple SUS display the updates on a web page?

You're not talking about seeing the SUS Catalog URL xml file in a browser are you?
I don't recall any way to get Software Update server to display the updates in readable format in a browser. If there is a way, I'd be interested in knowing since that would be interesting.

There is of course Reposado and/or NetSUS though.

Will that SUS Catalog URL xml file list all the available updates?

That will list every file Apple has available. Not what is only relevant to you.

If I read your post correctly, it will list ALL updates on that sever that's available, correct? If so, that's fine.

That should be the case. You can also fire up Reposado with Margarita and have a nice list as well on a web page, but that may also allow someone to modify the updates available.