That's the right location to be getting salem-res.jar, but the files in it might not be completely up-to-date.
The salem-res archive bundles a large set of .res files on all kinds of things - monsters, buildings, and so on. It contains 3d models, rendering code, and pretty much anything pertaining to everything.
HOWEVER, the client also checks with the server whether these files are up-to-date. If they are not, the client downloads the most recent version of the files from the server and saves it as a .cached file in ~/.salem
So the salem-jar file is basically a large cache of resource files that may not all be up to date, but which allows the client to pre-load a large number of them with little effort. It is not updated VERY often, as updating it makes everyone redownload it
This is the current state of the most recent salem-jar file: