Depends on the role.
It's a service celebration for those who have reached 5 year intervals throughout the Orlando area (Glendale and Anaheim each have their own in their cities).
For cast who regularly work the park in attractions, merchandise, food, etc, they may continue to work depending on their role/the need.
Other teams involved with the event (such as whichever event team puts it on) will work.
They also recruit CMs from around property to volunteer. I have been told by those that have volunteered in the past that it is possibly the coolest event to volunteer at, and it always has a long wait list.