I need to skim coat an existing painted stucco facade with stucco to a sand finish, will it adhere if I use an adhesive on the facade and in the stucco mix or should I rotohammer dimples in the facade every 3-4 inches
It largely depends on the finish of the "existing painted stucco", but most exterior finishes are rough enough that they provide a good mechanical key for anything plastered on top. You can use a PVA based primer as insurance, but [under usual circumstances] what is most likely to fail in the future is not the key between your most recent stucco and old one, but rather the key between the old stucco and the wall or the key between the old paint and the old stucco. So if want to rotohammer something, the best thing to do is use a wide chisel and remove the old stucco completely.
Since you're covering the old stucco eventually, you can test in a small and less visible area by apply your new stucco on top, let it dry/cure then try to remove it and see what comes off. You'll have to repair/refill a small area probably but if you want to be certain on the adherence issues this is what most pros do.