Having the tank overhang the stand like that is asking for trouble. It puts a great deal of stress on the areas that aren't supported by the stand. It's not a good idea.
And with respect to the dresser itself, by the time you get through adding gravel, a 100G tank is going to be closer to 1000lbs than 800.
There's no way I'd trust that thing to hold that kind of weight. It might-and I stress might-hold it for a period of time, but eventually it will probably fatigue and fail. I can assure you that being able to support a 1/2 ton static load was not in that thing's design criteria.
If you want to risk the cost and hassle of finding 125 gallons worth of water, gravel, dead/dying fish and shattered glass on your floor one evening, go for it. If not, buy or build a decent stand. Wood is a lot cheaper than cleaning up after that thing lets go would be.