A plugin will fire if the data is changed; it does not matter how the data is changed (as long as it is in a supported way). The plugin will fire if the data is changed by the entity form, from Javascript using the REST or SOAP endpoints in a different
form or a web resource, through a workflow, from a plugin, from a data import, or any other means of updating the data via the CRM web service APIs
Microsoft CRM MVP - http://mscrmuk.blogspot.com/ http://www.excitation.co.uk