I think there are more important tidbits here.
Often - but not always - a big artist performs when he/she/they are pretty much assured of winning some of the bigger awards. This isn't true at other award ceremonies, but seems a tad more customary at the Grammies.
Now, if the only mention of a "U2 performance" is this Bono/Blige duet, it strongly suggests that the rest of U2 might not be there or might not perform. Hence, I would expect no big victories (if any).
In contrast, if the remaining members of U2 are there and there is a U2 performance and THEN this Bono/Blige duet, it suggests U2 may be in for some of the bigger awards.
The thing with Blige is that her wailing just takes over the song. There's "Bono wailing", which he often does in unison with another, and then there's Blige wailing where she becomes the lead singer regardless of who else is present. She has a good voice and is talented, but I'd argue against her being a good duet partner. Hopefully this Bono/Blige duet is a Blige song or a night where Bono has hints of 1989 and can belt it out along with her.