Technically you don't need to have a current subscription to Jomsocial pro to use socialize. BUT the problem you will run into is the current version of socialize is made for the current version of Jomsocial which has just been released.
Purchasing the socialize template does not include a Jomsocial subscription. Please also note that the socialize template is a Joomla template for your site, and not an internal Jomsocial template
socialize.jomsocial.com