Not holes in the battery it self, in the battery house (where the battery located)
I see! If they fail; which there is a very slim chance they will, Li-ion batteries have a chance of either exploding on their own accord or venting, causing pressure and in-turn making the battery housing explode.
Nothing you do to the holder or area you hold the battery in, will effect what the battery does, it will only effect what the enclosure the battery is in does.
For instance, the Silver Bullet mod has two vent holes beneath the button. I have seen and there is a video for you to see on youtube, if you want, a Silver Bullet short out and vent through the button. What hole you drill, how big it is and where does not effect whether a battery melts, explodes or simply vents because that's all on the battery, not the location of it.
I believe that is why ECF started their battery hole guideline. As you can probably tell by the newest Buzz Pro iteration, the venting areas are far larger than previous models so that even in the event of an explosion, the mod might hold up and simply vent it out but if the battery merely vents, you have nothing to worry about because there is more than enough room for it to.
Most box mods don't even need to be considered for venting, because they aren't air-tight to begin with and in the event of an explosion, it would probably take the entire mod with it but as far as venting is concerned, you have no real worry as the boxes have plenty of cracks and holes for air to escape from.
It isn't something I would worry yourself over. Normal e-cigs like egos have adequate protection against battery failure and larger mods are normally built with proper venting in case of battery failure. You have more of a chance of winning the lottery and immediately being struck by lightning on July 4th 2013 than you do having your battery explode if it is properly protected.