It's not a question of the LOS we are concerned with, it's a matter of where the spell is considered being cast from.
Obscured states "It cannot be targeted from more than one zone away", the question is how does this interact with Vine Markers only one Zone away?
For example, if the Druid 4 Zones away uses a Vine Marker adjacent to an Obscured Zone, such as the Ethereal Mist tile, can a Stranglevine target a creature in that Zone?
Is the Vine Marker considered the Casting location (as it is adjacent and thereby eligible to cast), or the Druid (which is NOT adjacent)?
Also, has it been errata somewhere to state Obscured blocks LOS? The Druid Vs. Necromancer booklet doesn't state this. Are Obscured objects treated like Walls now?