If you push aside the whole leaves and recognizable leaves, you will find compost/leaf mould and most likely tons of earthworms. This is the stuff you want to use for your garden. If grandma is only using this area for leaf piles, scrape down to the subsoil -- GREAT rich topsoil under the compost. Put the leaf piles back on the subsoil to work their magic for another year or two.
From your description, I think you'll get plenty without using the undecomposed stuff in your garden beds.
For mulch, bag the dry leaves, dump them at home and run your (not mulching) lawn mower over them to chop them up. VoilÃƒÂ ! Mulch.
They don't blow away as much when chopped up and wetted down. I think mixed with grass clippings, moistened alfalfa pellets/alfalfa meal, and/or coffee grounds would be better, but not strictly necessary.
If you have more leaves, make compost pile(s) out of them, mixed with grass, weeds, and kitchen scraps.
IMHO, corncob bedding is too much brown. They also tend to get that black mold on them.
If you are making sheet mulched/lasagna-type beds, any of the material you mentioned would be a great addition. It sounds like you'd want a bit more GREEN in there though -- more grass/weeds, alfalfa pellets, hay, manure, unfinished compost, etc.