To use external DAC with any Android smartphone, you need (1) a version of the firmware that has USB-OTG driver built into it. Most don't since USB-OTG isn't part of standard Android driver yet. Highly doubt Sony Ericsson has it since it is an older model. (2) the smartphone itself need to has the proper USB-OTG chip inside, not just software. and (3) the external DAC needs to draw minimum power as most smartphone can't supply more than 100mA~150mA.
Yes and no. Many amp/DAC are designed in such a way that the DAC section draws most of its power from the USB port instead of battery (good reason to do it as it helps save battery life). So even you are not charging the battery, the DAC alone could already drawing too much power by itself. I do believe D-zero is fine, but E17 isn't.