I did not find a definitive answer, so i did what every reasonable person would do and just bought a used nikon and a canon version to test it :).
As slaves they both accept nikon and canon master TTL flashes, if set correctly.
Like Michael C pointed out, nikon flashes have a golden font on them, and canon is in silver.
Here I switched roles and accept ...
Is this Yongnuo specific model able to be fired in slave mode by another flash?
Yes. The Yongnuo YN565EX III has S1 and S2 slave modes that allow another flash to send the "fire" command to the YN565EX III.
In S1 mode the YN565EX III will fire when it detects a bright flash of light.
In S2 mode the YN565EX III will ignore the first set of short bursts, ...
Check your camera settings anyway, they have to be just right for AF Assist light to work. See D7100 manual page 233 about option A4, which has to be ON. And then it must be AF-S mode (or Single Servo if AF-A). And also, Center focus point selected in Single Point mode, or Auto Area mode. See page 233 to ensure they are still right.
It depends on which version of the YN565 you have. There are both Canon and Nikon versions. Neither version is cross-compatible with the other system with regard to TTL on camera.
If you have the Canon version, TTL should work on camera or off camera with a Canon TTL Master flash, such as the YN568EX II.
If you have a Nikon version, TTL will work off ...