Hi,
Populating fields in your form is definitely possible via web service. Qdabra's Database Accelerator (DBXL) features a couple of useful web services. To name a few, there's ADWS which allows you to retrieve users' Active Directory information, QueryDB which retrieves data from SQL - you can even do filtering, QuerySharePoint retrieves items from a SharePoint library/list. All these can be configured to populate your form fields on load. The best part is - you don't need to write code to use these web services! It also comes with its own submit web service which you can configure to submit data to SQL and/or SharePoint.
You can learn more about DBXL here. We also have a couple video demos which you can find in our video library.
Feel free to post any additional questions you may have. You may also email us at Support (at) Qdabra (dot) com.
Best Regards,