Actually the SPEs are not that similar to the PPE core. Their primary purpose is to process streams of calculations (greatly raising the processor computational abilities). I think its probably fairer to consider this to be a processor with eight tightly bound coprocessors on the same die (rather than a true multi-core processor). There really is nothing to prevent the SPEs from being used under Morphos while the PPE provides the bulk of the power to run the OS. As the PPE is the only true Power PC like element in this product (and there is only one on the Cell die), this would be where Morphos code would run anyway. The SPEs would just provide a great way to farm out concurrent calculations (they would make Morph a floating point beast).
Jim