Tim,
You can't created targetable channels through the API. As a result,
the answer is that, any channel you create in the API won't be
targetable, so a query to check the channel status here is pretty
moot. Its true that your publisher could go into the AdSense interface
and make the channel targetable, but its somewhat unlikely they'd do
this.
All that being said, this seems like a useful feature, so we'll look
at the feasibility of supporting it.
Cheers,
Justin
Google AdSense Team