To be honest, I'm not the best person to ask... My knowledge of it applies largely to the context of nuclear reactors, the conditions under which different types of corrosion/cracking occur for various types of steel and occasionally titanium. I just remember some elements of hydrogen assisted cracking and annealing in different materials. It's been a few years since I really applied any of this knowledge but here are the basic points:
- stainless steels are naturally resistant to hydrogen embrittlement
- I wouldn't expect it to be a huge issue for stuff on a car that's exposed to atmospheric conditions most of the time; for hydrogen assisted cracking to be a real issue, you'd need to expose the parts to elemental or molecular hydrogen (so basically acidic conditions).
- Electroplating will actually be the main cause of the problem as far as hydrogen assisted cracking is concerned, as you get molecular/elemental hydrogen forming at the metal boundary during the plating process - that's why I mentioned annealing it fairly quickly after you've done the electroplating work.
- Tensile stress will exacerbate the hydrogen assisted cracking process, but unless you've got conditions in which hydrogen is diffusing into the metal and degrading the grain boundaries within the component, this is largely not going to matter.
I think this is pretty much a non-issue to be honest, just anneal the stuff you electroplate within a few hours and you'll be fine. Mechanical failure of bolts and brackets is going to come from other forms of corrosion or stress fracture to be perfectly honest.