Hard to say for sure but I'd be willing to guess that DM handpicked MS (et al) to take part in this all for various reasons:
1. MS already has a criminal record whereas DM does not
2. Based on the gangsta/faux snuff video, MS is clearly a wannabe and I'm betting would be easily "bought" by the likes of DM. I think DM is a master manipulator, very conniving and cunning and a wannabe like MS, already known to police, could very easily be coaxed; be it with money, promises of help with making the videos so he can be a big star, or just the opportunity to act out being a real gangsta (kill someone).
I'm sure that DM figured if worse case scenario and the jig was up, who would stand a better chance.......Mr Silver Spoon DM with his piles of money and top notch legal team or an unemployed, deviant, low-life wannabe rapper who based on his role in that video has indicated an interest in the macabre and simulated murder/torture/gruesome violence.