No Bose system on the H3; it is either base or Monsoon.
I used Peripheral adapters.
Another hint, your VSS wiring may be in one of the connectors going to the radio. If not, it will be in the large connector under the right (passenger) kick panel.
If installing a rear camera, you can pick up a rear backup light feed in the left (driver) side A-pillar.
Must not have searched too well on the Hummer sites, there are quite a few discussions on the Z1 install. :D
If you want a pretty good write up for installing a Z1 in a H3:
http://www.elcovaforums.com/forums/showthread.php?t=19267