Supposedly you don't need the ulib lua to use ulx. Other admins in our server have ulx working.
ULib is an absolute requirement for ULX on the server.
Both also require some client side files, so both will require download when you connect.
You do not need to install Ulib OR ulx locally if you're running a ded server.
Listen server, absolutely will need them.
I do not know why you keep having to redownload them, other than you'd have to redownload each time you reinstalled your client.