[jeffy]

I've heard of exploding 12 oz bottles, but never a growler. Do you have any other knowledge or is your opinion pure speculation?

Speculation from observing the growlers.  You may have never heard of growlers exploding because it's not commonly used to prime beer.
One point though: some people think of growlers as the big swing top, handled glass jugs.  These are very sturdy glass and would most likely push the rubber gasket out before the glass was compromised.  I on the other hand usually think of growlers as the 1/2 gallon glass jugs with screw top lids.  My purely speculative opinion is that these would be too weak to risk bottle conditioning homebrew.