Well you're definitely limited by the sound quality a camcorder is able to reproduce. That much is certain.
But you can experiment with placing the camera in a position that provides advantages for the sound field as a whole. Try getting the camera away from the drums, as they're naturally going to eat up most of the headroom in the audio recording. Also, if you find yourself getting shrill high-end in the video, try experimenting by placing cloths of various thickness over the microphone input holes on the camera to filter some of the harsh bits out.
Really, your best bet is to place the camera in the optimum position for balance and sound quality as a part of the whole, which will require experimentation.
Just experiment with placement and record takes until you find the best possible position.
Edit:
If you're just planning on recording your drums for demo purposes, you can definitely mic them up and send through your mixer to your recording program... while at the same time recording the video. Afterward you simply separate the audio from the video recording in a video editing program and substitute it with your mic recording. It would simply be a matter of lining up the audio and tweaking to taste, then exporting the video with the new audio as a single video file.
You can probably find video editing programs for free on google.
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