Originally Posted by
fone
Take a look at the chart
here. You will see that Mileage Plus miles cannot upgrade SQ flights on star alliance upgrade awards.
As for the waitlist, I've heard SQ might fly with empty J seats even though there are people on the waitlist, not sure how true it is. Also SQ upgrade award books into its business saver award inventory (if using Krisflyer miles), not so sure about star alliance upgrade award, maybe it books into star alliance business award inventory (so you might want to look for those dates with availability).
This is not true. I upgraded a FRA-JFK SQ flight a few days ago to business class using my UA miles. I'm still waiting for availability on the outbound to upgrade that flight.
I believe the link on the *A website that you linked to is out of date. If you look at the UA page about the *A upgrades
here, you will see that SQ is on the list of participating airlines.