He's definitely out of key.
Oscar, I can't recall him singing badly for any other part of the show (though I haven't listened to it for a good while), which leads me to think it's just him having trouble with this song - they're by far the highest notes he had to do in the show at this stage. Furthermore, he sings it badly, to varying extents, in almost every recording I've heard - the fact that he consistently struggled with it seems to prove that it must've been demanding.
Yokohama - not as bad, but still not good:
https://www.youtube.com/watch?v=X5XEBQLeLTA
Brussels - top notes are flat, but he's otherwise fine:
https://www.youtube.com/watch?v=QtfymFm3Ko0
Kobe - a bit flat:
https://www.youtube.com/watch?v=xUgpfv88b2Y
Sheffield - a fairly flat at a couple of points
Bradford - top notes are flat
Manchester - he doesn't attempt them!
Cologne - the best I've heard apart from the Rainbow - he gets a few of the top notes spot on, but is a tiny bit flat here and there otherwise.
Brussels - top notes very flat
Milwaukee - top notes pretty flat
And of course,
Rainbow - he gets it perfectly in key, including the top notes. The Cologne recording indicates that he's capable of getting pretty close to nailing it, but it appears that he didn't sing it that well the majority of the time. I lean towards thinking the Rainbow version is overdubbed.