Music games such as Rock Band 2, Guitar Hero: World Tour, and [shudder] Rock Revolution typically rely upon controllers in the shape of the instruments they’re imitating to help sell the experience. But not rhythm-action music sim Ultimate Band - it sticks with the basic Wii remote and Nunchuk.
So, you don’t strap on a plastic guitar or bass and “play” it. You hold the nunchuk in your left hand, pressing the C and/or Z buttons like they’re frets (unless you’re on easy difficulty, which requires no buttons at all), and “strum” with the remote. You’ll also do other gestures to execute a “windmill” strumming motion, clap along, or hit the whammy bar. It’s not terribly accurate or precise – especially on bass, which has you tilting the nunchuk instead of some of the button presses – like a “real” controller would be.
Similarly, you don’t grab drumsticks and hit a downsized electric drum kit. You hold the nunchuk and remote in your hands and move them downward to hit drums, flick them to the side to hit cymbals, and make a swirling motion to “spin” the sticks in your fingers. It too, lacks in the accuracy department.
As for singers… well, there’s no mic, so you instead use the remote and ‘chuk to strike poses, wave at the crowd, clap along, punch the air, and so on. But you don’t actually sing. At all. Thus, accuracy isn’t really a concern here because there isn’t any.