Hey Simon,
The Edit Widget right now works of the operational layers(feature layers) that are editable. The operational layers are defined in the main config file. You can exclude layers from the edit widget by including the <excludelayer> tag in edit widget's config file.
Something like :
<?xml version="1.0" ?>
<configuration>
<createoptions>
<polygondrawtools>polygon,freehandpolygon,extent,autoComplete</polygondrawtools>
<polylinedrawtools>polyline,freehandpolyline,line</polylinedrawtools>
</createoptions>
<deletefeatures>true</deletefeatures>
<excludelayer>layer1</excludelayer>
<excludelayer>layer2</excludelayer>
</configuration>
Hope that helps.
--Sarthak Datt