Yes, wrapping a stainless header will hurt it or better stated, will increase the likelyhood of it cracking. Stainless has a very high thermal expansion rate due to its very low thermal conductivity and wrapping it cause more heat to be retained in the header and therefor causes more expansion and therefor more likely to crack. The other main problem with stainless is at the weld joint. If the joint is not back gassed or shielded in some way, shape, or form, you will get what we welders call sugar on the back side of the weld joint. This sugar is actually oxides formed from the reaction that stainless steels have with oxygen when heated to welding temperatures. These oxides can reduce the weld strength by as much as 30% or more. This weekened joint will likely crack.
As for SS autochrome header cracking, I have never really heard of there N/A headers cracking, but have heard of there Turbo headers cracking. I think that the main problem with the turbo headers cracking is the lack of support and and that they are probably using 304 instead of 321 or 347. 304 is perfectly fine for use with N/A applications as long as its welded correctly, but for Turbo app's, 321 or 347 has to be used along with again proper welding.