One thing to take into consideration is if your water level is not in fact level. Then the pressure on the supports of the dresser is angled and not straight down.
This could cause the dresser to "fold" in the direction of the force being applied to it.
You can get used pine stands pretty cheap usually. If you went that route, you could use those plastic storage bins with drawers, or just the hanging cloth sort with square spaces, and store your clothes inside the stand.
I'll 2nd,3rd, etc... the notion that putting a 75g on a dresser is not likely to end well.
From the description, there's a good chance the dresser plus tank ends up looking something like this:
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Okay, the picture didn't work.. It's meant to show a tank sitting centered on a dresser that is wider than the tank, such that the dresser's two vertical end supports aren't directly under any part of the tank.
This is supposition - if it happens that the ends of the tank sit over both of the end vertical supports directly it's not nearly as bad. But if this picture is close to right:
There are a couple issues here in terms of the dresser: One is that the outer two vertical supports aren't actually under the tank. They're not doing much. Most of the weight of the tank is supported on the single center support, with a little supported by the top, but likely not more than 100-200 lbs worth. (BTW - if the tank is close to center the top of the dresser won't visibly bow before the tank fails - the tank is quite rigid.) Obviously, a single center support like that wants to fall left or right, and will quite happily do so as soon as whatever fasteners are used fail. That brings us to the second issue. The dresser is probably held upright by the use of fasteners connecting those three vertical supports to the back. The back provides the lateral bracing needed to keep the vertical supports from falling to the left or right (via the fasteners, whatever they are). Essentially, it's those fasteners that are keeping the tank aloft. It's really hard to say just how much they can support before failing, but it's a safe bet that no one thought you'd sit 750 lbs up there.
BTW - If the pictures is right, and the tank is centered, it's counter-intuitive but it could be better to move it off-center so that it's being supported by two of the vertical supports.
In terms of the tank: They're designed to be supported around the whole perimeter. If it's as above, yours is only fully supported at the center of the two largest panes. If that's the case, it will be trying fairly hard to bow UPWARDS at the center (and let the ends fall). Seems to me there are two likely scenarios for how it would fail: the first is that the front or back glass will break catastrophically (CRASH - no warning). The other possibility is that the bottom and side seams, or bottom seam with the end of the front or back, will separate and it will develop a leak at the bottom that will allow the tank to completely drain. Not as dramatic, but the end result isn't all that different. Why you wouldn't see bowing before this happens: The tank is rigid. It can't bow without failing. As such, the dresser top also won't bow - it has nothing to cause it to do so.
Also, 75 gallons is a lot of water when it suddenly finds its way onto your floor, and it's going to go somewhere... (If someone lives under you they might not be terribly pleased with where it ends up going. ).