Hi!
Each game can be created by a team of up to 4 members.
A tester can absolutely be part of your team — in that case, they should be registered and will also be eligible for prizes.
However, if your team already has 4 members and someone is just helping you test the game (similar to how streamers get feedback from their audience), that’s totally fine too! They don’t have to register, but they won’t be eligible for prizes.
If you’d like, you can still have them register just to help the jam’s visibility — but it’s not required.