You sure can. The benefit to pallets is they allow for airflow under the wood. Stacking on stone will slightly slow the seasoning process, but should keep the wood from getting punky, so long it is in an area that drains well.
John one thing with a gravel pad you can make some huge production numbers if you split along side it...cause as you split it you're throwing it up on the pile on the return stroke. People don't realize how much time is used handling/moving/stacking wood before ya burn it. Piling eliminates tons of time otherwise spent on handling.
A long time ago our old timer neighbor that use to farm with horses told me about it...I resisted for years but finally got frustrated by my rows continually falling over. Piled wood on a 10x30 or bigger gravel pad has a pleasant rustic look to it until late in the fall we frame it out with saplings and make a walk in tent structure with very large tarps. You can get away with that out in the country.