I don't have one, but I imagine it will compress very slightly when the AGS is engaged, as all overdrive pedals compress the signal to some degree. But it will probably be less than the Sansamp, which may be designed to emulate the extra compression you get from driving a speaker cab for example.
You can double the 9v to 18v using a
Diago 18v adaptor along with a cable to plug into the tuner. Some tuner pedals have a max rated current draw on the output though so check the Tone Hammer won't exceed this (and it will likely draw double the mA from a converted 9v source as it will from a regular 18v supply).