We're very much of the mind come one, come all! :D Everyone is welcome to participate in all of our events, definitely.
The only thing I will say is, if you do choose to write or draw something for one of the prompts, you will need to join the community in order to post it, unless you want one of the mods to post it for you. But membership is open (or at least it should be--I'll have to make sure to check that!) and you can watch the community if you wish! And you definitely won't be required to join/watch to participate in the friending frenzy and the drabble-a-thon.