If there is a slope the water will not run upwards, and the water on the siding should run down to the ground and away as well. The siding panels should also be painted with outdoor paint also on the bottom so the water cannot penetrate in the cuts at the bottom of the siding. The small amount of time before it drains away will not cause it to rot as long as it’s treated in all the cuts, it’s the still water over time that causes the wall to rot.
Or do you mean there is nothing else behind these boards, so if you cut them there will be an open gap between the siding and the concrete?