The only downside of that technique may be the voltage getting too high at high rpm, and damaging the DC/DC. The pack never gets to much over 180V, but I have seen the IMA motor on the civic hit >220V when reved. We blew up a set of shop lights when the engine was reved. Some sort of top end regulation would likely be necessary.
I continue to find uses for the Prius NIMH subpacks that I have. The latest is to use two in series as a 12V starting pack for my John Deer backhoe, as well as the spare Dodge Caravan that my sister gave me. The little pack cranks like a standard size 12V battery, but only weighs 4.8 lbs.
http://www.99mpg.com/mikestips/
