Yes you can use ablative over hard (but not the other way around because the ablative sluffs off over time).
However it sounds like you are in the same boat I am, you really need to get down to gel coat and begin anew if you want it to look decent. I feel your pain!
I may go with that new Pettit bio bottom paint remover. It got a good review and try that. It is cheaper then 1500 bucks for a soda blast but probably more deadly
