Can these walls support bookshelves?
Not possible by just going into drywall.  The achors are not designed to bear that kind of load.  The reason this won't work is because of torque.  Drywall anchors are designed to support loads that are very near the wall (i.e. pulling, more or less, straight down along the wall).  Your shelf will probably have the load offset from the wall by a few inches, which will eventually pull the anchors out of the wall.  This is because of torque.   The farther you go from the wall the more torque you have.  While the shelf may hold for a while I would not trust it.
The torque on the anchors can be mitigated by putting in angle brackets.  These effectively redirect the load from the edge of the shelf back to the wall.  This is better, but I still wouldn't trust this shelf unless it is secured into something more than drywall.