Is the amount of health I heal from a hacked pack related to Sombra's charge gain

It would appear that her hacked health packs earn you ult charge rate the same way that Soldier 76 and Ana do. That is 1 point of ult charge for every 1 point of health healed.

• "Heroes gain 1 charge for every 1 point of self-healing done.
• Soldier: 76, Ana, and Sombra gain 1 charge for every 1 point of healing."

As with any other character capable of healing others, the amount of ultimate charge gained depends on the amount of health healed.

As of the patch on February 27, 2018, Sombra no longer gains any ultimate charge by having teammates collect hacked health packs.