As has been said before, the character doesn't get the half dragon template, it's simply poor wording.
from wizards customer service:
at 10th level, the dragon disciple prestige class states that the character takes on the half dragon template, is this simply flavour text, or does the character actually gain the entire template, including level adjustment, stat boosts etc. Common sense dictates that its simply flavour text and the character simply gains the bonuses listed, however the passage mentions the template, so its unclear.
-This is simply flavor text, since the character only gets the benefits listed in the prestige class. Good Gaming!
*Please quote this email in any reply.*
*******************************************
Chris
Customer Service Department
Wizards of the Coast
1-800-324-6496
*******************************************