Is it possible to power supply an EV3 hub through the battery slot with 10 V?
Yes. The EV3 technically only needs 5V to run. And just the EV3 by itself pulls around 200mA at that voltage. However, motors could be a problem. They can pull up to 1A when stalled, which could overload the power supply. Without knowing the technical specifications of the actual power supply, it is hard to say what it is actually capable of.