Absolutly acceptable. Your still playing along and singing live as you would with a band, IF the venue would pay a band. I keep them simple and as the names says in the backround of the mix.
It does open the door to a million mediocre singers who do very poor Kareoke Acts.
One of the most unusal and very good examples here is a drummer who's been here for a long time and works in one of the top bands. He also does a solo. Tracks with him playing drums and singing. People love him. Gotta love the name, his name is Mark Husbands so he calls his single act " The Single Husbands Band"