I have not looked into supporting jablum widgets and do not know what is involved.
The index.html page is generated from the default.htt file in the skins directory and it's relatively straight forward, simple web page. I guess you could modify this, but I am not sure how.
You could also add a menu item (see forum for adding links) and use that to interface with a widget. The menu structure is defined in the DPLMenu.xml file. Unfortunately this is generated each time and would need to be modified after the album is generated unless you really understand/know how to modify jalbum scripts (folders.htt)
To add additional menu buttons, you need to edit the DPLMenu.xml file after creating your album and adding:
For more help, please search DPL forum for answers....