Im running clean rom and group messaging works. The only thing is that the name and time stamp overlap at the moment. I flashed a theme from another thread that fixed the overlap issue but it got rid of all notifications that I received a text message. But group messaging does work to an extent.
For now I am running GO SMS, with ICS theme, it has Group texting option, working fine., But I hate third party text apps, they are slightly laggy, I just really like the stock AOSP Messaging app.