All child kernel launches are just like host (parent) kernel launches in this respect - they will utilize all available resources and are not limited to a single SM, regardless of the behavior of the parent kernel.
This is easy to prove with a bit of microbenchmark-style coding - have each block of the child kernel record which SM it is running on. Not sure how to do that? Search this forum for smid - you will find examples of function usable in device code that will tell you which SM you are executing on.