Toonami is a branch of Adult Swim. Adult Swim, in turn, is a branch of Cartoon Network. Cartoon Network is owned by Turner Broadcasting, which in turn is owned by Time Warner Cable.
Yes, it is a part of Cartoon Network, and for all the fools who voted No on the poll:
Toonami can not be considered separate, as it doesn't have it's own TV station and it is funded entirely form Turner Broadcasting's Cartoon Network. Now, if it was funded by itself, but was being aired on CN as an ease of access, then sure, it can be considered seperate. Yet it isn't, so it is a seperate branch.
Also, another question is which toonami you speak of. American Toonami or the Toonami channel in Hong Kong I believe.