Right now it looks like my username is being displayed based on the sn LDAP attribute. I'd prefer it to be displayName or gecos, is that something I can configure either via lightdm or ldap.conf?
I don't think that you can, at least not in lightdm. lightdm gets the user list from Gnome's accounts-service over dbus which I assume populates the list from ldap somehow. Perhaps there's a way to configure it in ldap.conf?