But it would be best to use the same camera - If you just can't do that, you should try to get your hands on both cameras well in advance of the shoot so you can see what the differences are - and use those to your advantage. For example, if one does better on wide shots than the other, it should be the "safe" shot while the other cam is handheld getting the close-ups.

Whomever is the camera holder needs to try and stay out of the other's shots - and the wide shot person can zoom in on a performer on one side of the stage while the handheld is on someone. Take lots of "b-roll" set up before, tear down after, maybe you can have the band walking in together onto the stage area. That way, if both camera shots are not good, you can cut in b-roll.

You MUST white balance the cameras under the same lighting that will be used during the shoot.

How are you getting the audio? If you expect a board feed, then make sure the audio engineer knows well in advance - and that they know how to properly get a discreet AUX send - properly mixed - to the wide-shot camcorder. Bring your own XLR cables and adapters. And headphones for that camera so you can hear what's going in. EVERYTHING on stage must be mic'd or properly connected to a DI box. If you can't do this, a good stereo mic about 20 feet from the stage will work... run the XLR cables back to the "safe shot" cam.

Lighting should be natural lighting - not reds, greens, blues stage lighting. Stage lighting is good for a show - not so good for video recording. If the band is doing this just for the video (no audience), then try to get them to play each song more than once - you may be able to cheat some of the edits - and it will look like you've got more than two cameras...

Good luck! The first time is exciting!