Can I use the Suunto 9 Peak cable with Suunto 9 Peak Pro?

No, Suunto 9 Peak Pro has its own cable. You can only use the new cable to charge Suunto 9 Peak Pro. 

The magnet in older Suunto 9 Peak cables is too strong, and they should not be used with Suunto 9 Peak Pro. If you connect a Suunto 9 Peak Pro to an older Suunto 9 Peak cable, you will receive the following warnings:

Charging not available.
Please use a compatible charging cable. 

You can easily distinguish the two cables by the shape of the contacts:

NOTE: You can, however, do the opposite and use the new Suunto 9 Peak Pro cable with Suunto 9 Peak.