SCT TRACON Controller reported departure SID traffic conflicted with aerobatic area traffic resulted in an avoidance vector below the MVA and a CFTT event.

Narrative

I just sat down to take the position. I was briefed that there was a departure coming off on the JADKO departure from SBD and that the REI aerobatics area was active. It is very rare to get a RWY 6 JADKO departure; so I had to pull up the map and remind myself where the departure would take them. I noticed that the track takes them right through the aerobatics area. I also then noticed that there was traffic in the aerobatics area. Usually; we don't see any aircraft in there; even though they owners call us and tell us they will be in there. This time though; I could see someone; which almost led me to believe it wasn't someone who was participating in the aerobatics. I called the traffic like normal when they were a couple miles away; but then I saw one of the targets make an immediate turn to the west and conflict with Aircraft X.I issued a traffic alert and turned Aircraft X south to try and avoid. Aircraft X was well below the MVA; at about 045 and the MVA is around 095.I believe the JADKO departure needs to be looked at in relation to the aerobatics area. The LOA with the aerobatics area says that the aircraft in the area are responsible for seeing and avoiding other traffic. While I believe that requirement is valid; I don't think we should be actively departing IFR traffic into an area of known aerobatics. In this scenario; all aircraft did what they were supposed to do; but the system failed.