It seems that most people are getting it to work, but for those having problems, I've been using Tao's Intent MIDlet Manager to run GMail mobile (and certain other java apps) without problems.
Might want to give it a shot for anyone that is having problems.
http://forum.xda-developers.com/showthread.php?t=286604
If 2.5 megs is too much to spare, I know for sure the older version (v10) works fine with gmail mobile as well.