Not unless one is a master to the other.
But there is a work around.
Create a new variable in the esp script you are writing, make it the same type as the var you want to check.
Find the quest name and variable in the other esp script you want to reference.
In your script add a line:
RunScriptLine "set myvar to that.var"
Then you can run your script using the same value as that.var.