Does Sosuke, Son of Seshiro's deathtouch-like ability combo with Matsu-Tribe Sniper?
The damaged creature will not be destroyed.

"Combat damage" is a specific subcategory of damage. The only way to deal Combat damage is during the combat damage step in the combat phase of a turn. From the Glossary in the comprehensive rules:


  Combat Damage
  
  
    Damage dealt during the combat damage step by attacking creatures and blocking creatures as a consequence of combat. See rule 510, “Combat Damage Step.”
  


Any other damage dealt, such as from the activated ability of Matsu-Tribe Sniper, is just damage; it is not "combat damage". Even if it took place during the combat step; it wasn't damage that was dealt as a result of attacking or blocking.