Yes. As of January 2015 all plans, including the free Sandbox plan come allow SSL/HTTPS connections.
This includes WebSocket and HTTP connections from clients and calls to the HTTP/REST endpoints.
As of January 2015 not all libraries (Client/WebSocket and Server/HTTP/REST) use SSL by default. So, you will need to set up the library to use SSL.
See the library documentation for the libraries you are using for details on how to do this.
Future versions of the libraries may be updated to use SSL by default.