Would cross training in Silat & ju jitsu be dangerous?

No, it's not dangerous. Sometimes it may become confusing when learning similar techniques. You may do it the right way for Jujitsu, but the wrong way for Silat. This wouldn't affect your effectiveness in a fight. It might just affect how quickly you rank up in the other art. Which really isn't that important anyway. I say take and learn as much as you reasonably can.