I don't think there is a cap for avoidance. Or atleast there wasn't before patch 1.6
Two reasons:
1. A hunter acheived 102% (w/ pre-nerf Juju Escape) and posted a video. Can't find it (Unfortunately, blizzard forum search says the word "dodge" has never been posted
)
2. Evasion tanking as a rogue feels a lot higher than 60%
