Aktivacija plugina samo ako ga tema explicitno podrzava.

functions.php

add_action('after_setup_theme','theme_setup');

function theme_setup()
{
add_theme_support('prefix-someCPT');
}

plugin.php

add_action('init','plugin_init');


function plugin_init()
{
    if( current_theme_supports('prefix-someCPTq') )
    {
      // plugin code
    }

}