I couldn't find anything about this specific situation, but will it work, and are there any side effects that could damage it? Also, will it treat the USB as a computer?
The charger will have the USB connection configured so that the device should not think that there is a host on the other end. As for the rest, I cannot put it any better than Olin already has. But long story short, as long as there is 5V at at least 460mA plus additional current required by any capes and USB devices there will likely be no problem.
I have a power supply tester. I have measured many usb chargers. Many cheap ones only provide stable power up to about 70% of their rated capacity. So from a theoretical point-of-view you should be able to power the beaglebone from a 500mA charger, but in practise that might not be enough.
Similarly, many cheap USB cables have conductors that are too thin for the small usb-powered computers of today like the beagle bone black and the raspberry pi. So make sure you use a high quality cable.
About damaging anything: Most chips that are powered by 5V actually specify 5V +/- 10%. But some will specify 5V +/- 5%. Many USB chargers will give out 5.2-5.3V: just that little extra power to charge the cellphone with... In case there are 5V +/- 5% chips on the beaglebone that 5.3V would officially be outside spec, but in practise I don't think they will die.