You may not "need" the resistors, but adding them to the 3.3v and/or 5v line might make the 12v more stable and less likely to dip under heavy loads. A little testing with a voltmeter should show if it helps or not. But if it works as-is, great!
lol, yeah, I should think so. 6 cells @ 2.1A only requires ~2A of power supply current. It's when you start charging large packs (4s/12 cells+) at high current (5A+) that the charger starts pulling lots of 12v current.