Is it possible to make world procs? If so, do/don't they work like regular 'ol procs?
Yes, you can.

Ermm... There is a makeshift example of a world procedure. Defining a var or a proc when it's not under anything will put it under datum/atom/.

The /atom object type is the ancestor of all mappable objects in the game. The types /area, /turf, /obj, and /mob are all derived from /atom. You should not create instances of /atom directly but should use /area, /turf, /obj, and /mob for actual objects. The /atom object type exists for the purpose of defining variables or procedures that are shared by all of the other "physical" objects. These are also the only objects for which verbs may be accessible to the user.

/atom is derived from /datum, so it inherits the basic properties that are shared by all DM objects.