I do belive this thread was about weapon models, not player models.
So if you are refering to weapon models: I don't belive there is any skeleton stuff involved with making a weapon model. I really am not possitive, since I haven't made any weapon models yet.
But if you are talking about player models: Yes, you need to know about skeleton's. It's not so hard if the group is using animation that refers to bones with the same name / structure as the original gordon model. As long as the bone names corespond, you shouldn't have much trouble. (Ask a animator for the name's of the bones if your not sure what they are... You don't have to if you decompile a model from ESF or whatever mod into you milkshape program and check that way!)
Please don't flame me if I gave out false information, again I say I'm not possitive about this since I'm only farly new to modeling myself.
Hope this helps!