SpiderOak does not follow symbolic links when doing a backup scan. The reason for this is that there are too many possible ways to create a recursive backup loop using symbolic links and it leads to a number of very weird potential problems. Those often include a great deal of confusion at restore time, confusion regarding usage reporting ("Why is SpiderOak using 2.8 GB to backup this small folder??") and so on.
In SpiderOak releases prior to 2.0, there was a bug in the user interface that did not correctly show symlinks as being unselectable. That is fixed in versions 2.0 and newer.