Dear Dag,
Could we please wait to hear this confirmed by someone from the Spacewalk development community ? You may or may not know that what Red Hat ships and is called Red Hat Network Satellite, is in fact using spacewalk packages, and a seperate RHN package that rebrands Spacewalk.
I am an active member of the Spacewalk Community for quite a long time (not seen you there btw.). At work we are using both, Satellite or Spacewalk, so please go ahead and fool someone else.
Spacewalk is the UPSTREAM for Satellite, so development is quite faster. Packages that are concerned to be used with Satellite could as well work with Spacewalk but may lack of features (as stated before).
In my opinion, if CentOS wants to be compatible with RHEL, it needs to be compatible even in the parts that may or may not be useful to its users. Let the users decide whether it is useful to them or not, even if the majority will never use Spacewalk.
This has really nothing to do with RHEL compability, or do you want to manage your CentOS clients with Satellite?
Best Regards Marcus