I don't see why not, i power them from PC USB ports, 2A USB charger, 2A Power Brick and via a hacked USB cable and a buck convertor from a 12v lipo down to 5v
Only thing i have found is the three nano I have, are more sensitive to noise on the supply line the higher the voltage is.
I have been testing with the 8x8 LED matrix displays and found they work ok at about 3.8v but as the voltage gets higher you have to put a big cap (2200uf) across gnd and 5v pins else the noise causes to program to crash and/or the cpu to reboot.. Very Unstable 
Hope that helps imk