Will I be able to record master-quality (e.g., to submit for film-TV pitches at TAXI) recordings using my iPad? Also have a Zoom H2, have Shure SLR mics, can put the guitar in directly. Would like to be able to use rhythm tracks occasionally too. What's the best resource for advice on making the most of iPad recording? (Have had songs on TV before but those were studio recordings.)
No, mastering is a complete post-process which require know-how (mastering engineering is itself a discipline separate from recording- and mixing engineering, although it can be combined).
That being said, you may or may not be able to get a good vocal recording from a recording device without much processing. If you mix in instruments you will need to consider mastering.
There are aspects such as levels, EQ, compression and other factors which determine if it's fit for broadcast. But not without saying it also depends on the medium which in it is broadcast. For instance, mastering a news report isn't required at all. Is it broadcasting amateur recordings? then they won't expect mastered content and will process it to a certain degree themselves.
Unless you have access to a studio setup specifically for mastering and you have the know-how, you may want to hand over the recording to a mastering company. On-line services that offer mastering of a recording comes in a bunch, some good, some bad, some expensive, some cheap.. it's not a simple choice. But look around for references and a fair price.
If you want to make master quality recordings, you're going to need a quality set of monitors fed by a much nicer digital to analog converter than the zoom. Also don't overlook the importance of the room you are recording and mixing in.
With the right hardware I think that the iPad could do what you want. It has a lot of really neat soft synths and sequencers, and Wavemachine's Auria is a real deal DAW with some amount of real plugin support. So I think that the iPad could get it done, but just like any studio set up the hardware, and the room is more important than the computer.