I would store all your spawn points in an array. Then when you want to spawn a zombie have a function that loops through your array and checks each point against whatever set distance you want from the player. If it is smaller than the distance add it to a temporary spawn point array within this function (local variable). Once the loop is complete, have it select a random index from the temp array of desired spawn points. Then have a return node return this value from the function. After you can feed that location into a spawning function or spawn from within the previous function if you so choose.