You'd probably not use it at this stage. I'd guess this is more about getting 16 core chips to developers to let them try using them. Handling all the cores is the difficult bit, vectorisation is relatively simple compared to that.

They had a similar situation before. The G5s they used for the 360 have Altivec but it's not the same as the version in the 360 itself. IIRC the version in the 360 has more registers and additional instructions.