Hi
The iFrame approach worked fine in the mobile app. Definitely enables viewing Vimeo vids in the mobile app when domain privacy is necessary - also saved time of uploading/maintaining vids in Moodle if you already have a bunch in Vimeo and want to manage them all from Vimeo.
Depending on whether the Vimeo embed code is in a file on its own or dropped into an existing Moodle page, can take some CSS and/or JS work to position the video correctly - for example, initially used some existing material that was in a Moodle page and didn't realize the video was displaying correctly - it was there but existing CSS and elements were causing it to seem hidden.
Hope this update helps others!
John