Can I split audio before it gets to my sound recorder?
Technically if you want to be sure that you are getting the highest possible audio quality you need a pre-amp that you can use to split the signal. But the effect is going to be very small.

When you split a signal you are relying on the impedance of the two input devices being high, and the output impedance of the source being low, and everything being even across the frequency spectrum. Most modern equipment has high input impedance and low output impedance, so that's generally fine–you will get a couple of dB drop because you're splitting the signal across two outputs–but what could go wrong is that you will get e.q. shifts because the impedances might not be perfectly flat across the whole range of frequencies.

However it is unlikely to cause much of a problem for recording interviews, most likely it would only be a real issue if you were recording something like musical instruments. In an interview things like the room acoustics are going to have a far greater effect on the audio quality. Either way, a splitter cable is only going to cost a few bucks, so it's worth a test.