the only upper-level vs creator strife has been at the film studios
no, but some of the writers are pretty candid, even if they have to fuzz up details a little bit.
bendis, for example, has made mention that "this editor made that choice", but it's always been within the comics domain, not "well, disney said we had to do this"
and yes, that doesn't mean it doesn't happen - just that if it does, it's likely either innocuous or everyone is very much afraid