I think the reason why Israel doesn't see PKK as terrorists is that they are only limited to Turkey and targeting Turkish installations elsewhere - it is not an international Muslim terror organisation - thus is not recognized by Israel.
This is nonsense,why European Union (all EU countries) , U.S.A. and United Nations recognized it as a terrorist organization ? Also there is something you don't know that PKK is becoming more islamic as they cannot get Kurdish people support by communist ideology.So they tended to islamic idelogies.I would not get surprised if it became another islamic terror organization right in the middle of the middle east.