We have been working on using the REST API to import content into an email / template with mixed results (errors on import which we are working on now). Other apps allow a neat way of an HTTP/S import but Marketo doesn't seem to so looking for ideas/suggestions.
Our APIs are pretty extensive. You should be able to do pretty much anything you want.
Check out the resource above. You can create a new Email Template programmatically, put in whatever HTML you want, then create a new Email using that template and send it out, all programmatically.