AdeptiCon has a pretty loose Model Policy these days. The bit about manufacturers reads:
Your army should be primarily constructed of models from the given game system and the appropriate model range(s). Supplementing your army with models from outside the game system is acceptable but should NOT be the norm.
We found that no matter what you said in regards to
GW or Forge World models, people still brought Ultraforge, Armorcast and what have you.
GW had those requirements because they were the ones running the
GTs - makes perfect sense, but independent conventions/events don't necessarily have to adhere to such a rigid format. The above advice is spot on though - always check ahead of time. There isn't any standardization across events these days - things will change from event to event.