Wether a package ignores certain filetypes depends on the author of the package. There are various ways in which a plugin author can accomplish this (e.g. check the syntax and bail out, use a ViewEventListener with an appropriate is_applicable, etc).
Usually the console is a good place to check if there are any packages that do something unintended. (View -> Show Console).
By default all packages are "running". That means all of their commands get loaded into memory, all of their EventListeners get instantiated (once) and all of their ViewEventListeners get instantiated if applicable (per view), all of their snippets get loaded into memory, all of their keybindings get registered, etc. The plugin author has to make sure that their snippets and keybindings get masked correctly.