Hi jennh, I've never grown an Adenium, but horticultural oil will kill scales. I've never heard ofCaptain Jacks Dead Bug Brew either... it certainly has an intriguing name tho'
I'm not familiar with that product but it is well known in the organic community that you can collect pest insects and whir them in a blender to make a slurry that will control that pest when sprayed on it. No one knows quite how it works but it does.
OK I looked it up. Capatin Jacks Dead Bug Brew is basically Spinosad. There has been some controversy over the use of Spinosad. Although it is an organic derived from a soil fungus it has some undesirable side effects such as killing bees and predator insects. It has to be used very cautiosly to avoid doing harm. I'm not sure whether or not it would be effective against scale. That's a hard one to kill. Probably dormant oil is your best bet this time of year.