If it's a template like Half-Dragon or Half-Fiend then leadership is based on character level
So a 6th lvl Half-Dragon Paladin is 6th level for the purposes of Leadership
However a 6th lvl Bugbear Fighter would add the Monster HD as levels to the class levels to determine character level. Thus the 6th level Bugbear fighter would be 9th level (3 levels of Humanoid + 6 levels of Fighter) for the purposes of Leadership.
The problem with the Half-Dragon Paladin vis a vis leadership is that his low character level vs his ECL make his initially recruited cohort suboptimal.
Taking our example the 6th level Half-Dragon Paladin is equivalent to a 9th level human PC. However he can only recruit up to a 4th level Cohort (Character Level - 2) whereas a 9th level human paladin could potentially recruit a 7th level Cohort. While the 4th level Cohort should gain levels faster than a 7th level Cohort the fact that it can be no closer than 1 level behind the Paladin will always keep the Cohort less powerful than a cohort for a +0 ECL PC.
Considering a bunch of Paladin class abilities are level dependent (Turn, Lay on Hands, Mount) the +3 LA really negatively impacts the Half-Dragon Paladin in a PC setting. The increases to abilities hardly negates the loss of level related power. If you do choose to do this character I strongly suggest using the ruleset for buying off level adjustment.