I mean, yes, this is a where these sort of things get increasingly more complex.btw, about the Hulk thing. i'm a little confused how b&m could be able to not be involved in the launch systems at all. I mean, the coaster is designed to launch out of the lift hill- could it even clear the barrel roll without a boost? surely they had to be at least somewhat involved in the launch system planning and then after, the various testing phases once the launch has been in place. I understand that they didn't manufacture the tire drives or whatever, but don't a huge amount of companies not manufacture everything in-house anyway? i know we're doing simplified analogies here but I just can't really believe that b&m would be like 'yo here's that peculariarly shaped giant chunk of metal you asked for, go nuts! (hey fred, how are they even planning to get this going? beats me aye)"
I suspect it was more a case of B&M saying to Universal "here's the weight of the train (plus probably a load of other technical data for chassis dimensions, materials, etc, etc), and it needs to be going 40mph by the end of this bit of track". Universal will have then taken that information to some supplier who designed/provided the hardware. There would have then probably been interfaces back to B&M regarding sensors, integration of the hardware (where do the bolts go, exactly), etc.
On something like Thunderbird, B&M handled that relationship directly with the launch manufacturer - Holiday World had nothing to do with it.
For the car analogy again (people seemed to like that) - if you're buying your own tires, Ford would tell you things like rim size, available wheel space, car weight, torque at the wheels, etc - you would then have to liaise with your supplier to get a tire to fit and work. Normally, Ford would just handle all of that themselves.