If the avatar is smaller than the maximum size in both pixels and mb then it should load up and animate.
If the animated avatar is larger, and vbulletin has to shrink it to fit then you will loose the animation.
Try uploading it and see
If you go to the usergroup manager and choose the usergroup, then about halfway down you'll see under Picture Uploading Permissions > Can Upload Animated Avatar Make sure you set this to yes
Good Luck