Wrong on both counts. While you can require a mission to use DLC Premium Content, most creators, including BI themselves, make DLC ownership optional. The only exception is use of Tanoa from the Apex Expansion. If you use this terrain, players must have Apex in order to join the server. If a player wishes to avoid the buy DLC prompts, they need to be aware of the premium content assets and avoid using them. (Note: premium content vehicles allow non-DLC players to occupy only passenger seats, they are banned from crew positions.) BI does not hide any content from any player. See the official BI DLC Policy.