Vampire abilities are granted to the creature automatically, they don't get 'vampire levels'. He's a vampire, which means he has all vampire abilities. The only thing that would affect would be Durkon's HD, if he still has 14 levels of d8, and 1 level of d12.
Now that being said, it would not be unreasonable for Rich to say that Durkon can't access some of his vampire abilities as a result of being a brand new vampire. Maybe he can't turn into gaseous form or shapeshift yet because he hasn't figured out how. Maybe he doesn't have DR yet because his body hasn't had enough time to change to that degree.
There also could legitimately be some drawbacks to Malack's use of that staff to hasten the process. Normally vampires don't rise until 1d4 days after death - it is not unreasonable to think that Malack's spell might have cost him some vampire abilities (or they won't manifest until the time Durkon would have risen as a vampire normally).