You do have to add them to your friend list first. To do that you cluck your avatar, select friends, then click "Add a friend". Then you can search for your friends username, highlight it and click add.
I've seen some claims of people cheating, but I don't see how it is really possible. There have been claims that one person has multiple account names being played at the same time, or that one player had friends in the game ganging up on the one making the claim, etc.
But really, if you are playing auto matches given the number of people who are online and looking for a game the likelihood of ending up in the same game with a friend or another one of your accounts is very, very small.
As far as manipulating the dice rolls, they would have to hack the server or something like that to do it and I can't see that as being worth the effort.
As the other post said, sometimes the dice roll in your favor too. You just tend to notice more when they aren't getting rolled in your favor.
Yes, I have always gotten a response. They are usually very helpful. It may take a while, especially if you emailed them over a weekend, but they will always get back to you. That doesn't mean they can necessarily fix your problem given the bugs in the 2.0.x updates, but they do help if they can.
I am on a newer iphone and recently having the same issue with the dice stats being zoomed in and unable to see the graph of all the numbers. Was working fine before latest update. Please let me know if you figure out a solution.