Are we asking if these hosts are huge fans or just fans? That's a little tricker to say, but I think Kimmel, probably Fallon and DeGeneres are genuine fans.
Apparently U2 were at the top of Corden's wishlist for Carpool Karaoke and he saw them back in 2015. He had a story about that because Pierce Brosnan was there too and was apparently really rude to him.
I guess Fallon is a fan (I'm not really a fan of his or Corden for that matter), but he does seem to genuinely like them. But who knows? He's tough to decipher.
I think Kimmel is a fan, he did mention when he interviewed U2 in 2017 that seeing them and Springsteen in concert is a religious experience. He also talked about listening to a concert from the parking lot when he couldn't get tickets.
I remember U2 were on Conan O'Brien's show back in 2005 for an entire week, which was a big deal at the time (they also did with Letterman in 2009). I think Conan likes them well enough, they were a big pretty get for his staff from what I recall. Letterman, yeah could go either way, but he probably likes them.
Still no idea about Seth Meyers and Colbert probably likes them well enough, though maybe not a huge fan.
All that said, when U2 breaks up or a band member(s) dies, I wonder what the reaction will be. I imagine a lot of "fans" coming out and heaping praise on them endlessly. But that happens with just about every big artist when they die.