How do we stop the heartbeat module from recording node update activity for certain specific content types we have created?
seems like you use D6 since you mentioned Commons. I've only used Heartbeat in D7. Click on the "heartbeat streams" settings and you have an option for "Choose message types you want to deny from display". There you can select the ones you do NOT want to record. Repeat that for each of the streams.

Also, checkout the "heartbeat templates" for "add_node" and "edit_node", there is an option "Disable the message - Defines whether this message template is disabled from logging and viewing."