What kind of "poe convertor" do you have in mind?
mUPS specs state that mUPS comes with a Gb PoE injector as standard accessory, which I assume is intended to provide power to mUPS via ethernet. RB devices, that have PoE in, usually don't make any distinction of particular power supply port ... so I would expect mUPS will charge connected battery regardless if used PoE or power jack.