Yes, multiple artists can certainly collaborate on a piece that will be submitted to SWAG. However, we do have some rules regarding where a collaborative piece will get displayed. Generally, these fall into two categories:
All Artists are Guild Members: If all of the artists working on a piece are Guild Members, then the piece will be displayed in one of the collaborators' gallery. It is up to the artists working on the piece to decide into whose gallery the piece will go. Credit for all participants should, of course, be given in the description.
At Least Some of the Artists are Non-Guild Members: If one or more (or all) of the artists working on a piece are not Guild Members, then the piece will be displayed in the Community Gallery. It is up to the artists working on the piece as to which artist will receive primary credit for the piece (i.e. whose name will be posted as the artist). Credit for all participants should, of course, be given in the description.