If you really want to get all nerdy about it, you can calculate the pressure of the wood on the pavement and compare to the pressure a car puts on the pavement. Pavement designers assume that the pressure on the pavement from a vehicle is the same as the tire inflation pressure. That is, your car presses down on your driveway at around 32 lbs/in^2. Probably somebody on this forum knows the tire pressure of a big truck, which I assume your driveway could handle. You can figure out the weight of the wood, divide by the area of the wood on the bottom of the pallet, and that will give you the pressue a pallet will put on the pavement. I'd use only the area of the main 2x4 beams of the pallet because the weight will be on those and might not spread out over the entire pallet area. If the two pressures are more or less the same, you're OK I suspect. Of course engineers get into more depth regarding axle loads, etc., but just the pressure on the pavement should give you an idea if the wood is too heavy.
So, oak is about 4000 ppounds per cord. If you stack 4 ft high on a 4x4 ft pallet, that is 1/2 cord or 2000 lbs. If there are 3 2x4 cross members, each 4 ft long running across the pallet (seems pretty standard), then there is 1.5 inches x 3 boards x 4 ft long = 216 square inches of contact. 2000 lbs / 216 square inches is less than 10 psi. i think you're OK.