As SydneyKid has said, if the design is right and the manifold is supported properly with flex pipes then all the manifold has to do is its job!!! (spooling the turbo, not carrying the weight of the whole exhaust system!)
Anyway, I use a Trust Tuned length stainless Manifold, To4R Turbo, Greddy Wastegate and have had no problems with cracking, more thab likely due to the fact that the dump pipe was designed with flex pipes in it.