Bloat was always a concern in my house with the bullys but now that Athena has made herself a home in my heart it is an obsession! The #1 killer of Great Danes is bloat so I have studied this almost as much as I studied kidney disease with Abby.
There is no great evidence either way on raised or ground level feeding. The theory about bloat is that air causes the stomach to twist which is why some believe raising the bowl, making them eat slower is a decent preventative. There have been studies that completely discount everything we think we know about GDV, they say everything we know is wrong. But these studies were all done on deep chested breeds who were prone to bloat in the first place. I've spoken to many Dane breeders and large breed vets about this and they all say something different about bowl height.
What they all agree on is this...
Feed smaller meals. Twice a day is better than once a day.
No activity one hour before and one hour after meals.
No WATER one hour before and one hour after meals.
Feed a grain free food that doesn't expand too much during the digestion process.
Once an animal bloats, the odds of it happening again increase by 75% unless a gastroplexy is done
Gas-X strips are your new American Express Card.... don't leave home without it.
To test if your dogs food puts him or her at a greater risk for bloat you should take a cup of food, put it in a bowl, cover it with warm water and tightly cover the bowl with plastic wrap and let it sit for an hour. After an hour if the plastic wrap is puffy the food you are feeding creates a lot of gas (gas in the bowl, gas in the gut) Also, it's bad if the food has absorbed all of the water. This mimics how the food expands in the belly during digestion. If the food expands too much it can cause the stomach to become heavy and lopsided which makes flipping easier.
The stomach flips, gas builds up and up and up. Most times the spleen also flips along with the stomach! Without immediate treatment you lose your best friend.

Gas-X strips or any anti gas medication can buy you some more time to get to the vet but there is no guarantee. I like the strips because they are easy to carry in my pocket or wallet, they dissolve instantly on the tongue and I don't have to worry about shoving pills down her throat.