Yes. All sound corrections can be set up independently for the left ear and the right ear: audiograms , equalizer etc. That is important because many or most patients have a different left/right hearing loss that has to be considered to achieve a well hearing help.
That is difficult to say because both categories a very different. The advantages of an iPhone solution are: * the high processing power of iPhones/iPads/iPods enables high quality algorithms. * the microphone covers a wide bandwith. * the solution is much cheaper because the device does mostly already exist. * profiles can be changed self-reliant.
That is not generally to say. It seems that this does depend on the used iOS and/or the used iOS device and/or the used bluetooth headset. But the use of a bluetooth headset is NOT recommended anyway because this adds a time delay to the sound that can result in disturbing echos. And it's just the point that hearing help itself does not produce echos.
It is more recommended to use an iPhone, because the iPods microphone is built in the head phones cable and may produce some noise. Although hearing help has got a noisefilter this cannot eliminate all disturbances. The iPhone owns good mircrophones that usually do not need any noise filtering.