Does anyone know if the accessory shoe on top of the handle (audio unit) is a "hot" shoe?

I had to rebuild a mount for a LED light source that mounts on an accessory shoe, and I had to make it with metal to support the weight of the unit. I'm wondering if sliding a piece of metal into the mount will have any adverse effects on the camcorder. I have already used the cam with my part in the shoe before it occurred to me that maybe I should have checked this first. The battery life seemed normal, but that's not to say I may not be harming the cam (or the battery) in the long run.

The documentation simply refers to it as accessory shoe, and you'd think they'd advertise it as "hot" if it was, but I just want to be sure I'm not damaging the cam by using my custom mount.

While not totally familiar with your particular camera, I will say that I haven't seen a real "hot" shoe on a video camera is so many years that I can't even remember when I did see one. (possibly never but then I might just be forgeting the 1 or 2 video cameras that actually had a true "hot shoe")
The "hot shot" eminated from the old days of still cameras and was a way to sync a flash unit to the shutter. Not really something we worry about using video cameras. So I would say you aren't hurting the camera at all electronically speaking that is.

I believe Don is correct. "hot" shoes were really never an issue on video cameras. The only camera I can think of right now that has a "sort of" hot shoe is the Sony VG-10. It has two shoes, one a normal cold shoe mount, the other a Sony smart shoe to accommodate and sync a Sony flash unit for stills shooting.
That mount is a proprietory design though, it won't accept non-Sony equipment

You are correct. The manual does not say anything about a "hot" shoe on this camera, it is just a mount for third accessory.