When I click your above link in Windows 7 IE9 NO KIOSK, I see the following
in the address bar. Don't you?
http://youtube.googleapis.com/v/XITHbsUUlYI?fs=1&rel=0&autoplay=1

So, if I used that as my link:
http://youtube.googleapis.com/v/XITHbsUUlYI?fs=0&rel=0&autoplay=1
which happens to work by the way with no flip-flopping in kiosk mode,
would that be likely to continue working long term. Which is all I
meant by safe.

Note that I certainly would use fs=0 as the button it displays would not
do anything anyway.

Thanks