Personally, I would be worried about the seams being brittle and whether or not the tank was designed to hold water, some reptile tanks that look like fish tanks, aren't designed to hold large amounts of water. Other than that, I imagine it could be cleaned well enough to not be a problem.
IMO, that tank holds by far too much water to trust without knowing the history. If it was for sure a fish aquarium, and I knew it was less than 3 or 4 years old, I would concider it based on its condition. If it was 5 years old or older, I would be concerned about the seams, silicone drying up due to heat lamps or chemicals they may have used to clean it, and such.