No, Light vs. Dark ONLY divides people when during Trials of Heroes mass PvP battle.
Though members of the same allegiance that choose to get married can either
a) be married in Glastheim Abbey if Dark or
b) be married... ....I forgot where, but some place all holy and shiz, if Light
Those are really the only two differences in the allegiances aside from aesthetic things.
If you snoop around in the Control Panel (
link) you can find out how many of what class there is, but don't trust it completely when it comes to when those classes are actually played.