Not 100% sure on all allergic reaction mechanisms, but I can tell you anything involving blood moving up to the surface isn't going to happen.

In hives and other rashes, the raised red surface is because your microscopic blood vessels react to let more blood flow into the area.

When you are dead, those tiny blood vessel walls are no longer reacting, and the blood isn't flowing.

In fact, the blood settles on the bottom of your body as it's no longer being kept moving and muscled back from where gravity pulls it - this is called liver mortis.