SCCM using an existing WSUS server

This is possible, but a little cumbersome.

Fortunately, this blog post provides a step-by-step walkthrough of how it can be accomplished: http://syscenterstuff.blogspot.com/2010/12/sccm-migrating-from-wsus-to-sccm.html

There is a whole bunch of possible issues here:

• Is the WSUS actually operating on the defaults ports as you say ? It could be using the alternate config.
• The pfSense suggest the WSUS server is in another subnet as the clients. Are you sure the URL used in the policy is actually valid from the clients perspective ?
• Is the policy really deployed to the clients ? Check if the registry keys are created on a client computer. GPUPDATE /FORCE is your friend.
• On a client run "wuauclt /DetectNow" from a command prompt. Check WindowsUpdate.log (in C:\Windows or c:\Winnt) to see what is happening.