Andrew, I'm sorry that you found the documentation to be confusing. Perhaps we can update it after we conclude this interaction. I'm also sorry that I didn't get a chance to call you today: it's been a very busy day!
The bottom line is that we have tried to normalize behavior between SIP and H.323 endpoints. The statement you quoted was correct: that if you don't have a SIP endpoint or SIP trunk involved in a call, CM will not send the call to SM. Calls to/from SIP endpoints will always traverse SM, but there are subtleties that would complicate the use of Collaboration Environment call intercept snap-ins in ways different than those used by H.323. For instance, Collaboration Environment snap-ins sequenced between a SIP endpoint and CM will break certain CM features. Also, on calls between 2 SIP stations, calling party snap-ins could be invoked after CM has done its termination processing such as call forwarding or setting a voicemail coverage timer.
We are working to rectify these shortcomings so that call intercept snap-ins can be invoked on all calls in the enterprise, but we're not able to do so yet.
If you have any specific suggestions for wording changes in the whitepaper to make this clearer, please let me know and I'll be happy to work on updating it.