A small update, since this thread keeps getting bumped again and again by users upset at the removal of events. It appears Roblox wishes for UGC to work as a replacement for events in the future.
Q: Will there be a way to reward players in-game with UGC items?
A: We definitely want to allow rewarding UGC items in-game in the future - this has been an important part of events as long as they’ve been around, and we want to empower developers to make awesome games and events with prizes. However, since UGC items cannot currently be free, we’re still working on the best way to enable rewarding them as prizes. Additionally, UGC catalog items can currently be sold through games just as Roblox-owned catalog items can.
Source: UGC Catalog is Now Live!