Through the TEI projects page, I came across a project at the Illinois Institute of Technology called “Voices of the Holocaust” which is an “online collection of interviews with Holocaust survivors conducted in the immediate aftermath of World War II.” The project relies on TEI encoding to “provide a structured data model for the transcriptions, which allows various manifestations of the interviews (text, audio)–as well as other types of content (metadata, GIS, scholarly criticism)–to be integrated into a dynamic, robust presentation for the user.” (http://www.tei-c.org/Activities/Projects/vo02.xml).
On the “Voices of the Holocaust” website, there is a more in-depth description of its use of TEI (version P5), “which is used to encode not only the text itself, but also the biographical, historical, and geographical metadata related to the transcriptions, interviewees, and content; scholarly commentary and footnotes; and time-code information from the audio files to facilitate text-audio synchronization […] The Glossary of Terms, Glossary of Camps & Ghettos, and GIS data are also stored in TEI XML format; information from these files is included within the interview files using XInclude.” It also states that <oXygen/> XML Editor was used for text encoding, and mentions that built-in support for the TEI schema is included in the program (http://voices.iit.edu/project_notes).
Lastly, the “Voices” website offers a link to a sample TEI XML interview file, which can be found at this URL: http://voices.iit.edu/xml/voth_project_tei_example.xml
All in all, the project is fairly out front regarding its methods of TEI encoding.