Is it possible for a Nintex workflow to monitor a list on a different site collection to initiate a workflow?
You can use the Query List action to query other sites collections. You'd need to use the CAML editor and then enter the URL of the site you're wanting to query. You could then have a site workflow run on a schedule to query that list and perform some action based on the results.
Could you use a web service to start a workflow? Nintex Workflow Web Service Methods
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