I am not sure it will work the way you describe it (transparently).
The valid connection checker (this can be either a sql statement in the *ds.xml file or a class that does the lifting) is meant to be called when a connection is taken from the pool, as the db could have closed it while it is in the pool. If the connection is no longer valid,
it is closed and a new one is requested from the DB - this is completely transparent to the application and only happens (as you say) when the connection is taken out of the pool. You can then use that in your application for a long time.
The exception sorter is meant to report to the application if e.g. ORA-0815 is a harmless or bad return code for a SQL statement. If it is a harmless one it is basically swallowed, while for a bad one it is reported to the application as an Exception.
So if you want to use the exception sorter to find bad connections in the pool, you need to be prepared that basically every statement that you fire could throw a stale-connection Exception and you would need to close the connection and try to obtain a new one. This means appropriate changes in your code, which you can of course do.
I think firing a cheap sql statement at the DB every now and then to check if a connection from the pool is still valid is a lot less expensive than doing all this checking 'by hand'.
Btw: while there is the generic connection checker sql that works with all databases, some databases provide another way of testing if the connection is good; Oracle has a special ping command for this, which is used in the special OracleConnectionChecker class you refer to. So it may be that there is something similar for MS-SQL, which is less expensive than a simple SQL statement.
