Yes you can. I've been in several at one time.
Resolved: question
For diamond membership, you can play in an unlimited number of tournaments at once. Here's a chart with all the information:
http://support.chess.com/Knowledgebase/Article/View/85/0/how-do-membership-levels-free-vs-premium-affect-access-to-tournaments
Hope this helps!
You did send el-checko to maintain your diamond status, right? If you did, that means you can join lots of tournaments.
Dear Mr. Rat see here and eat more cheese and be quiet.
http://www.chess.com/membership.html?c=account
can u join more than 1 tournament at a time i'm ratatouie