Speed controls support a certain number of volts. It does not care if these volts come from a lipo, a A123 cell., or a hamster running in a cage.
The monster pro will work with A123 cells. It should handle 6 of them very nicely. However is has trouble with 6 lipos, because lipo have a bit more volts per cell.
You must have a A123 charger to charge them.
usually people buy them on ebay for around $100 shipped for a dewalt pack, see here to take a part and stuff:
http://www.rcgroups.com/forums/showthread.php?t=587606
http://www.rcgroups.com/forums/showthread.php?t=599316
Now, when you freshly charge a lipo, they are 3.7 volts per cell.
A123 when freshly charged are 3.3 volts per cell.
So they are less powerful then a lipo. They are also heavier for their power to strength ratio.
(1) A123 cell is a little bit bigger then a C sized battery.
A123 are not as volatile to explosion, they can also charge at a higher "C" rating. You could charge a A123 pack in 15 min
See this post on some more ideas for A123 and it has a picture of them:
http://www.rc-monster.com/forum/showthread.php?t=9397