Teams vs Participants
I think it would be nice to have the option to distinguish between Teams and Participants. Your participants are teams that can be randomly selected for a match. But I would like to enter Participants as players from which Challonge can randomly create teams and finally matches. An additional option would be to divide the player in two groups where Challange could generate teams with players who are not in the same group.
Example: For a Table Soccer Tournament players can sign in a list and could select their experiences (Beginner/Advance). Based on that list Challonge could generate teams consisting of a beginner and advance player or teams that consist of beginners only or advanced player only.