I know the nudi you are talking about....Berghia verrucicornis. There are a couple problems with them though. All they eat is aptasia, and after it's exhausted they die. Also from what I have hear, they are not cheap.
Given how severe your problem is, I would almost consider cutting off your corals and ditching the rocks into boiling water, but I would use this as a last resort.
#1 you kill everything else on your LR as well, making it dead rock, and really of no use for natural filtration any more.
#2 I think given the opportunity, the shrimp may take over, if you get caught up. Maybe skip ALL feeding of your tank for a few (2-3) days (don't worry everything will live). This should send the shrimp into a scavange mode, and they might start attaking the aptasia.
I still would keep using aptasia x to try and get as many as you can, but I would try and get the ones away from the corals with it first. hose them down to the stalk on the glass, and clear those out first. Leave the ones in the rock for now...get the easy ones first. Give it some time, there isn't going to be an overnight fix on this.