The ServiceNow alert actions should already be available to be triggered as adaptive response actions from correlation searches, provided that the permissions are set correctly so that the ServiceNow alert actions are available to all apps. However, in order to get them to appear as an option as an ad-hoc adaptive response from the Incident Review dashboard, you'll need the param._cam, which you can add on your own instance:
Follow the docs to do this here: http://dev.splunk.com/view/enterprise-security/SP-CAAAFBG
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