I have seen this funcationality done, but not in conjunction with a Nintex Form.  So yes it is possible for SharePoint to receive such.  The app was responsible for capturing the handwriting and convert it to text and then the text was push to SharePoint via web services from within the app.  How will this work with Nintex is a good question and I would think its possible since Nintex is sitting on top of SharePoint.

I'd say go for it and let us know what you discover.  I'm curious to hear about this specific use case.

Thanks,

Eric