Can I use a different IP for the admin CP as I use for the Raq's main domain?
How can I set it up?

You can access the admin CP using any IP or any virtual site present in the system.
http://anyip/admin or http://anysite/admin redirects to the admin CP.
The easiest way to add a new ip to the system is to create a new virtual site and in the IP address field put the ip you want to add.
I can't unserstand why you want to do that, could you explain it?

I want to have one IP for the server administartion and another for the website and virtual sites management

You could try modifying the rewrite rules section in /etc/httpd/conf/httpd.conf

There is a rule for rewriting http://anysite/admin to https://anysite:81/.cobalt/sysManage/index.html
You could try having it to rewrite only for the ip you want and disabling it on all other IPs and virtual sites.