I had to rebuilt the rear Joytech hub on my 2008(ish) Schwinn High Timber after I broke the axle:
My hubs have a integrated dust cover which consists of a rubber diaphragm that is pressed into the end of the hub and has a opening for the cone:
The cones on the new axle have dust covers on them (the old ones did not), but the opening on the hub is larger than most I presume:
At first I was going to remove the pressed on one from the cone. I figured if I left them both on there then the rotating integrated one would be sliced apart from the sharp edge of the one on the cone. So what should I do in this case, or remove the one pressed on the cone? A quick look at the hubs on JoyTech's website suggest that all the ones with the rubber diaphragm do not use the metal ones on the cones. Considering this, I'm leaning to removing the ones on the cones.
I just happen to have a new stock spare wheel for this bike that I'm going to use in the mean time. Here is the photo of it as a reference: