Homebrew Question

A homebrew application that I use is hosted on google code, and edited regularly. In the downloads section, each revision is uploaded as a .dol file for access by SD card, and a .wad file for installation to the Wii. All of the .wad files have a notice that that they are "untested and could brick the Wii if installed". So, I tried using the .dol file and ran into zero problems with the program. Does this mean that it is safe to install the .wad, or could it still be dangerous?

it could still be dangerous. The banner could be bad. HOWEVER, you may be looking at a program which is not supported here, which I have personally used for legitimate purposes, and it should be fine to install. That being said, you'll also be fine if you have Priiloader or Bootmii, in which case you can get to the homebrew channel and uninstall the bad WAD

The WAD is a channel that will appear in the system menu. It could cause a banner brick, regardless of the fact that the program works. However, if you install Bootmii as boot2 or Priiloader, it is completely safe to install the WAD, as you can easily fix a banner brick if it occurs. Do not install any channel WADs without either Priiloader or Bootmii installed as boot2.

There really isn't any reason to install the WAD, unless you like wasting tiny bits of space on frivolous things already doable by the Homebrew Channel.

Is there any Windows program which can check if a .wad has an invalid banner?

If you run it through CustomizeMii (just choose to use the internal dol and leave all other settings untouched), it should ensure the banner won't brick you. But its still essential to have protection, its just plain stupid to install channels without at least priiloader.