I don't know if any specific ICs are used in there.
But if you really want to know, you can always ask the designer Yves Usson, he certainly knows.
You can find him on http://hackabrute.yusynth.net
On that site there are no schematics yet of the microbrute, but there are for the minibrute. As the microbrute is a scaled down version of the minibrute, I assume the electronics are not that different. So you can have a look at the minibrute schematics to see what is used.
Hope that helps,