Technically provided the voltages are the exact same you can run an alternate power source. The primary issue is the amperage. If you actually draw more amps through the new power source than the device can handle (eg, the circuitry and wiring) you can cause the USB hub to overheat, die, and potentially (in worst case) catch fire from the overheating.

The quality of the hub will also likely dictate how high the amperage can go as a low quality hub is likely to use low-end materials and poor quality solder work on the contacts, potentially causing additional issues.

(As an example I bought a couple 7 port hubs only to find that it was actually two hubs cascaded (eg 1 hub connected to another internally) which caused the second hub to fail entirely, as well as poor solder work, incomplete/missing contacts etc. Both of those are now junk as they don't function)