… depends on how you define it; or who does the defining 
I am referring to people ‘collecting, organising, editing and annotating documents’ – in the broadest sense of all terms (including ‘documents’). to me it seems DT is geared to just that. and I take from the webpage its demography is “lawyers, teachers, journalists, researchers, students, and authors” – I´d have a hard time seeing a lot of difference to the way knowledge work is defined in current day sociology.
as to your second point (‘about the video files themselves’ and ‘embedded chapters’): good question. the question as question was part of my initial insertion. I am myself not sure / knowledgeable enough about how the chapter / marker logic is (coherently?) translated in technical file logics – after the demise of the MPEG-7 project. I think there are different technicals formats around, most not standardized yet. it seems to me to be a similar situation as to the one in which subtitles were before SRT really took the field. this is why my initial contribution asked for a knowledge exchange on this, rather than asserting anything specific here.
the general motif was first asserting the importance and indeed ascendance of timeline based reference for modern knowledge work. and then turn to the technical side. and turn to the community here, and the distributed practices, knowledges, and familiarities. looking for real discourse.
what I can say (and have also dropped in the parallel conversation around Sanjivs concerns ), is that there seem to be tools by now that allow for working with chapterization of videos in a way that is also compatible with YouTube and Vimeo chapters (ChapterWorks SX). but thing is: I do not know what format / technology is behind that. which is why I ask the community and people who could know…