You do not need Crowns to participate in events, @TheTreeofDoom.

Crowns are optional if you want to purchase tickets or other goodies at the Impresario NPC merchant.

However, having the required content (zone DLC, dungeon DLC, or Chapter) can often be a prerequisite to play.

For example, the current "Lost Treasures of Skyrim" Event is focused in Western Skyrim & Solitude ... so having the Greymoor Chapter is required.

Other events, like the upcoming Witches Festival (late October), take place in the base game. So, for that event, all players can participate if they choose.

Bottom Line: If you don't have Greymoor Chapter yet, you can still purchase event tickets and items with Crowns (if you don't want to miss out on some of the rewards). But that is totally optional.