I have a wifi device (IP camera) that doesn't work (wired ethernet is Okay).

As there is no way to investigate from inside the box O/S (closed source), I would like to capture the traffic, if any, between the camera and my wifi router, which is also closed source ...

I have looked around for sniffing software for linux, but they seem to be focused on cracking IDs. This isn't what I'm looking for, as the traffic is set to be unencrypted.
What general purpose sniffer would you suggest to capture the wifi dialog between these boxes ?

"ethereal" works quite well. Make sure you set the wireless interface to Monitor mode before you start it up.

Yes, ethereal (or wireshark) is the most advanced sniffer that has a gui.