Yes. As stated, a shotgun barrel alone is not NFA restricted. A person buying the barrel and in possession of the other parts to assemble a shotgun would be in violation of the NFA.
While good advice, it is not necessary to contact ATF on every topic regarding firearms. Most of the NFA is clearly written and you can read it yourself at ATF's website. If there is something you don't understand, write to ATF and get a written response.