That's what I would do; if PHP doesn't abort with true HTTP errors, then catch every possible error at the PHP level, set a 4xx or 5xx error status code and respond the error message, otherwise set a 200 status ( its the default so you dont have to do anything ) and respond a 'success' message or whatever else it is that you want to respond with on success.

I forgot to mention, if using headers manually; you must set the status and header before responding any other content - this might mean you have to buffer output until you're sure that the response is error free, or decide very quickly whether the response is an error or not. Also, you'd have to mark en entire response as either an error or a success, so, you wouldn't be able to mix error messages with success messages.