It's been a long time, but when I was initiated into Order of Omega, it was pretty much just to honor the top 3% of Greeks (by GPA and activities to an extent) on campus...my chapter was not active at all, other than to hold initiation once a year...and that included the process of selecting new members (yes, you have to be invited to join...).
I think some campuses have active chapters though--you can find out more at
http://www.orderofomega.org/index.html