You have to listen for the uke. If you weren't sure what it was, it could get by you.
We have the same thing happen with our band. I play with a drummer, bass, two guitars and piano. My uke has a pickup and I can match all of them for volume. When we play back our practice sessions, we can hear the uke, but agian, if you didn't know what it was, it would be hard to pinpoint that sound -- it isn't something you expect with a rock band.
There are several commercials (and UU threads) running with ukulele soundtracks. Once you know the sound, they're easy to pick out. Otherwise it could just be a friendly guitar.