Hi Paul,
You can create nodes dynamically using the data entered by the user. It is not necessary that you have to load DiagramControl using the .edd or .edp files.
Please have a look at the sample in which nodes are generated dynamically and linked together:
http://websamples.syncfusion.com/samples/Diagram.Web/5.2.0.25/I39211/main.htm Please let me know if this helps you out.
Regards,
Raji