Mouseferatu
Hero
While, again, I have no inside knowledge and thus cannot make any promises, I see no reason why it shouldn't still be possible to add class levels to monsters. It should still be possible to add X (levels) to Y (monsters), no matter how Y was created.
It may not be entirely smooth, in terms of figuring out how much XP the monster is worth or what level of difficulty it is--but then, neither was total CR in 3E, really.
It may not be entirely smooth, in terms of figuring out how much XP the monster is worth or what level of difficulty it is--but then, neither was total CR in 3E, really.