Hi,
did you register the driver and all its companion libraries via the Add directory button as described here.
If so and the driver still does not appear can you please have a look at the KNIME log file if you can find an error during loading of the driver maybe by searching for the file path you used for registering the driver.
I just tried it with a vanilla KNIME 4.0 the following way.
Downloaded the driver and extracted it. Moved the ucanaccess-4.0.4.jar file and all files from the lib folder into a single folder.
Registered the folder in KNIME 4.0 via the Add directory button of the Database (legacy) page
Once this is done I can select the net.ucanaccess.jdbc.UcanaccessDriver in the Database Connector (legacy)
Bye
Tobias