I use Kamailio for register and Asterisk servers for processing call.

Asterisk accept all calls from Kamailio and dont know nothing about users and their passwords.

I think this is simplest way for integration and using best from both applications.

The way you mention is the approach I use in most of the cases. The respective tutorial tries to give hints on how to plug Kamailio in front of an existing Asterisk deployment without disturbing it that much.

Cheers,
Daniel