Of course it's okay. They are just people and people make mistakes. Sometimes I feel like doing a certain thing and when I look at it months later, I think to myself WTF. It's a mood thing really, and te grow with those mistakes.
The other people who responded basically took the words right out of my mouth, so, yeah, not every singer likes every song they sing. Like Amy Lee from Evanescence, she had song the song 'My Immortal', I remember in an interview that she was in where she stated it wasn't one of her favorites, as she felt nothing while performing it. It happens. They're human like the rest of us, we all make mistakes and wish that we hadn't done things that we had done in the past.
Not necessarily I mean just because the singer doesn't like the song, doesn't mean that the listerns also won't o even the other band member won't. A singer can sing something very artistic/wonderful but it still many not be the singer's cup of tea. And yet it's still a pretty song.
When they're making the song, it should mean something. It's okay if the song doesn't always have the same meaning as it did when it was written. But I personally think it's bullshit to make art if te don't mean it. Kinda defeats the purpose.