1) DAL uses the standard "TSO to = specs batch DB2 interface" to communicate with DB2. Security is supported via standard RACROUTE calls. The VTAM server is a multi-user server that runs as a batch job (or a started task) and that has a VTAM API front-end that controls access. The user needs a valid ID and password, but does not log on to TSO. Instead the user issues a "logon applid(_____)" command to connect to the VTAM Server. With the CICS passthru, the user logs on to CICS and requests the CICS transaction which uses APPC (LU62) to connect to the VTAM front-end of the server. CICS can be at version 1.7 but the PUT for LU6.2 support must have been applied to allow DAL VTAM Server access (version 2.1, or better, of CICS includes this LU62 support).
2) Stored procedures are kept in the DAL.AUTOEXEC file that is installed with the Server. (Only two sample database connection procedures are shipped with the server.) You can create your own procedures and store them there for general use. See the Server Installation Guide for more detail on this issue.
3) APPC communication from the client to the VTAM server (as opposed to from CICS to the VTAM server) requires the Apple product SNA*ps and its APPC Gateway. This connection type will allow for faster data transfer because it is not using the LU2 protocols (3270 data streams) but instead the LU6.2 protocols (APPC). Only the direct access method ("?ogon applid(______)") to the VTAM server supports this protocol. The CICS passthru requires 3270 protocols (since CICS requires them) and therefore is supported by all the current network connections that support TSO server access.