I think for small gigs like you describe, if the venue knows what's up and, to some degree, the crowd too then it is def not cheating. I know some folks on this forum are able to do local gigs and use backing tracks. If the audience is coming to see art or to dance they may not care.

On the other hand, I don't think backing tracks work if folks are coming to see the performer specifically. I know personally, if I am paying to see an artist perform I definitely do not want them to play prerecorded material!