Not sure that'd work. Lets say it was $700k, and I adjust it by 50k to remain anonymous (I'd be more inclined to pick last year's salary, so at least it was a true number, but anyway). I'd guess my company only has a few engineers post $500k, so chances that I'm alone -- and identifiable -- by posting a 650-750 range seems high.
The bigger problem isn't my individual case, but how many other engineers are in a similar range and never participate in surveys like this. I don't know.
I would assume you make that much because you bring that much value to the company. I doubt anyone who's a supervisor of yours would see it, care if the saw it, would be willing to fire you if they cared, and would be willing the risk a lawsuit for firing you for an illegal reason (in the US it's illegal to discourage salary discussion). Worst case scenario you leave a toxic environment behind and get a similarly paying job at a better place.
The bigger problem isn't my individual case, but how many other engineers are in a similar range and never participate in surveys like this. I don't know.