Eh, I still like to think it was only elites. You need to be aware that there are elite ships and brute ships, the two races do NOT share ships with each other. Thel vadam, being the commander of all the forces attacking reach probably had complete control over which ships formed his "personal guard" so to speak. And of course being an elite all of his "guard" would be elite ships.
So when he followed the POA to halo with his "personal guard", then they would all naturally be elites.
[Edited on 02.16.2011 7:57 PM PST]