Do uno (or did they ever) accept travelcards on these services? Something tells me that they did (approx 5 years ago, when I lived there) but I don't recall 100% either way. I guess they don't now?
They used to, yes. They must now have decided that the fixed amount TfL would give them for each use is not worth them accepting them.
This timetable from 2009 (http://www.unobus.info/previewpdf/614preview.pdf) confirms this. Note that you find this very easily with a google search but there's no indication it's no longer valid.