Yes, this happened to my Teddy recently. He had a reaction to a possible sting from a hornet and a reaction to a shampoo that we used for the first time.
The reaction caused a bunch of hives on the back end of his body. A few scabbed over. The scabs came off and his skin was perfect underneath.
As long as your baby is not developing new spots, and as long as the scabbed areas do not look infected, your pup is likely on the road to recovery.
Have your groomer stick to shampoo and other products that you know do not cause a reaction.