It seems that validations that have to do with more than one field are kind of hard to do client side with the gem so I found a way that seems somewhat clean and easy to implement so I added it to our fork's wiki.
Feel free to pull it in your own wiki if its an ok solution (or inform me of a better one).
Common validations for multiple fields
@eirc as this is not a bug I'm going to close, there is value to the wiki entry, please feel free to add to the core wiki
up: Shared validations for multiple fields