I am sorry to hear about your grandson I understand your concern and quite frankly I am going to be a little cautious answering your question and concerns. Speaking from experience (my daughter had acid reflux as a child) and working with infants and toddlers the same I have never heard of reflux causing marks that resemble raw skin? It is usually a symptom that will heal itself. There are a few things that you can do to help the situation.
Elevating the head of the baby's crib or bassinet.
Holding the baby upright for 30 minutes after a feeding.
Thickening bottle feedings with cereal (do not do this without a doctor's supervision).
Changing feeding schedules.
Trying solid food (with your doctor's approval). I am trying not to read through the lines on your post. I can say this if you feel your grandson is not being well cared for you can seek the proper guidelines in doing so. I would start by sitting down with the mom and asking direct questions. I would also attend a scheduled physician appointment and address concerns with him/her.

Acid reflux cannot cause deterioration of the skin like that. Even if he did vomit on himself, the acidic juices would have to sit on his skin for a while to cause the effect that I think you are describing.

He has some sort of dermatitis, unrelated condition, or he is not being given the attention he needs. I don't want to say that is is abuse, but I agree with breck that you should ask the mom some direct questions and see a pediatrician.