For concert taping, you'd probably either have a set up that uses stealth-type micro mics or full size condenser mics.
The micro mics will run on something known as plug-in power to provide the necessary power (say anywhere from 1.5v - 9v). Many handheld recorders provide plug-in power, but almost none provide it at high enough voltage that they can be used for concert recording (the M10 might be the exception, I don't know). To get the needed PIP voltage, most people use battery boxes or mini-preamps with PIP, like the ones from Chris Church Audio or Sound Professionals.
Otherwise, people are using full size condenser microphones (which can be small diaphragm or large diaphragm, and the small diaphragm can still be very small footprint mics like the DPA 4022). Condensor mics run on something called phantom power, which originally was 48v, but some mics accept phantom power between 12v and 48v.
The phantom power is provided by a mic preamp, that can be separate or integrated into the recorder, such as the 722. So the 722 in your example provides the P48 phantom power as well as mic preamp and recorder provisions. As such, it is a bit odd or unnecessary to have an M10 attached to the 722, as the 722 can do everything, but as you note an M10 might be used as a back up to the recording capabilities of the 722. In this case, as a back up, the 722 would need to continue to function and provide the P48 and mic preamp capabilities for the M10 to have anything to record (and as such the M10 isn't providing much of a back up, since if the 722 dies or runs out of battery power, all bets are off).
All analog-input recorders will be providing some amount of gain, or at least be routing the signal through a gain stage (or more than one gain stage), even if no actual gain is being applied. And any analog-input digital recorders will be providing an A-to-D conversion (analog to digital) function to get to the digital recording. As such, in your example, the recordings on the hard drive of the 722 and CF card of the 722 will be identical, but the back up recording on the M10 will be different, as it will have whatever analog output stages of the 722 (which may/will/do differ from the input stage of the 722 to the internal A-to-D), plus the different analog gain stage of the M10, plus the A-to-D stage of the M10.
The M10 has a very nice analog input section and A-to-D section, but it will be different than the 722, so not an exact back up.
So the M10 attached to a 722 provides some level of back up, but it would be odd other than for back up to attach an M10 to a 722 and use the 722 only for the mic preamp functions. In that case, it might be better to buy a Sound Devices USBPre 2 to use as a front end for P48 condensor mics with output to the M10. The USBPre 2 supposedly uses the same mic preamps as the 722/744 and the same A/D as the 788, so if you wanted the quality of the 722 front end but wanted to record to the M10, the USBPre 2 would make more sense. At that point, if you wanted recording back up you could use the Zoom or get a second M10, etc.