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I don't think it is feasible for an elephant-sized hyena to hide on the actual hunting grounds, least of all from predators that have similar excellent senses. 

What it should do is to lay low some distance away from good hunting grounds, then watch the sky for carrion birds. If a predator has successfully killed its prey, vultures and crows etc are likely to appear circling in the sky, waiting for that predator to finish its meal.

That's where your giant hyena starts running in the direction of where the birds are circling. It doesn't need to be all that stealthy, just big and intimidating. It doesn't run away with the meal, it just claims it for itself and eats it on the spot. In case it manages to catch one of the predators too, all the more food.

For this tactic to work, the carcass needs to be large enough so it can't be carried away by the predator who made the kill, which is most often the case.

Evolution might benefit the giant hyena if it indeed often kills the original predator too. That way it leaves more food behind for carrion birds and end up living in symbiosis with them.

With this approach, eye sight might be important though. Possibly hearing too, if it can hear carrion birds screaming from a long distance away. Speed might be important.

I'd assume that the female of these giant hyenas raises the pups alone - then the pups simply follow in tow best they can when the adult female starts running, but stay in the background until mama has secured the food, much like the behavior of other predator pups/cubs.