I don't see why there would be a problem with using the colored submersible lights in a whiskey barrel fountain. As long as they remain submerged when lit, you should be just fine.

Sure ya can. They do it at the garden shows all the time. You can even submerge a light in a birdbath. Just make sure you use a liner because whiskey barrels rot really fast if you use them for a water garden.

You can use your submersible light and any water fountain as long as the water covers it. I have not ever tried this but I bet it will look pretty.

You bet you can! We have some on display (I work in a Garden Retail Center) and they look really cool when we're closing the store at night and most lights are out.