What makes Lone Druid "work"?
Lone Druid is generally played as an offlane hero, this is because he's hard to catch out since his Spirit Bear can farm while he stands behind somewhere safe.
During the laning phase, do Lone Druid players have both units selected to last hit the same creeps, or do they use both units to attack individual creeps?
Usually doesn't matter the method, as long as your can get those last hits in the lane, what I do usually is send the Spirit Bear to harass and zone while i use the hero to last hit early on. When you have decent points into Synergy, the Spirit Bear gets really good damage especially with Quelling Blade, from there i'd play my hero more defensively to not die, or harass with my hero and farm with my Spirit Bear. I wouldnt attack individual creeps or keep auto attacking, you end up pushing out the lane too much, leaving you exposed to ganks.