SurveyMonkey's API is currently read-only and does not allow adding users to email collectors. And option you might consider is pairing SurveyMonkey with MailChimp. MailChimp currently has docs on how to use it with SurveyMonkey here: http://kb.mailchimp.com/article/setting-up-your-surveymonkey-mailchimp-integration/
You could also create something like the MailChimp API in your own application by adding a unique ID to links you send to your respondents by appending ?c=UNIQUEID to the end of a web link collector URI. Then, in your application, you can send any email invitation you like to potential respondents and use the unique ID to correlate users with responses.
You'll need to request the "custom_id" by adding it to the "fields" array in your request to get_respondent_list in order to that unique ID back from SurveyMonkey using the API.