I just found this tool, it lets you create new and custom metadata profiles for filetypes. I tried it with epub and was able to enable basic fields like Authors, Title, Category, and Subject. Values are set through the Details tab in the File Properties window, and show up in the relevant columns in DOpus.
I played a bit with the custom profiles feature, and was able to get additional data fields to show up in the File Properties window, but could not figure out which corresponding columns to add in my lister to see that data. Maybe full DOpus integration isn't possible?
Anyway, just throwing this out there for discussion. Not sure if it's worth investing time in, but I've been looking for a way to tag my epub files and see that data in DOpus columns, and this came up as an option...