If you have this file, which is definitely the result of exporting dynamic items to the wsc file, then you definitely do not need to insert these items into art.mul. You have to have them there. But just to give you an idea, wsc can be used to convert dynamic items to static ones. This means that you will insert them into the statics files. You can use UO Fiddler for that, but I would use a mulpatcher that works very well with it. Furthermore, if you use ServUO, it has built-in commands for converting dynamic items to static ones. You don't need any other external program or this wsc export.