I see Halo as a game played by customers and that game also has story attached to its campaign play. I have no problem separating the non-story parts of the game from the story. This isn't a problem for me even if I'm in campaign. If someone wore a pig helmet whilst playing co-op with me I'd just know that the helmet was what my friend chose to wear.

I wouldn't worry about the reasons that "real" Spartans in the real haloverse would wear such a thing or how it reflects on the professionalism of Spartan 4s. Thinking along those lines just undermines the haloverse for me.