Addendum:

>> what I would like to know is whether IBM's stock A2 core (as used in
>> the PowerEN and Power BQC chips) has it. I ask because I've
>> read conflicting third party statements on that matter (and no statement
>> by IBM itself).

> http://www.theregister.co.uk/2011/08/22/ibm_bluegene_q_chip/
> As that detailed article doesn't mention AltiVec/VMX for the A2 core
> I assume that it's not there.

Found an IBM source:

"The A2 processor does not support vector single instruction, multiple data (VMX) instructions."
http://www.redbooks.ibm.com/redbooks/pdfs/sg247948.pdf (page 77 ("61"))