Ouch. Well that'll make me think twice before just 'nabbing' somebody else's model, as they put it.
I'm trying to understand where they're coming from - they spend months and months working on a large product, the way they did, release it as part of their mod, and then require that people use the bayonets if they're running that mod only. In short, they expect that no one will unpack their addons, take their intellectual property (in the form of models and animations et cetera), and freely distribute them in a whole range of other addons. They also expect that if anyone wants a general purpose bayonet for any situation, they'll have to make their own.
Now, as far as i can see, the only thing stopping that from happening, is the thoughtfulness and consideration of the authors' wishes by every single person who decides to download their mod. Any one person could do what I mentioned before, taking and redistributing, with virtually no consequences. At the end of the day the community is a relatively anonymous place.
So whilst I would never take things from their modification, for example, or in fact from anyone else's when they were not entirely happy with me doing so, I also find it rather unrealistic to expect that no one would, ever. On the other hand, public opinion (community opinion in other words) might be a stronger force than I'm allowing for, and prevent this from happening. Certainly, nothing else will, unless the team wants to spend time and effort developing a foolproof encryption system. Personally I would allow for this, and anything I make will probably be for free distribution, with the usual 'you are free to modify this but give the original author credit.' That usually works pretty well, and it's spotted if someone seriously violates the rule.
Having said that, though, if I'd just completed a project of that magnitude, I might feel a little differently, and more jealously guard my IP.