My custom web clipper works in a similar way. The clipped content is saved to a separate folder before being imported into DT, through a script that is automatically executed. The script also sets custom metadata in DT, using data from the clipped content.
I don’t create a new document directly in DT, because AppleScript frequently messes up with HTML source codes, for reasons I could not determine. Not the same issue as yours. However, the solution could be identical.