If you have hidden any contact and now want to unhide, just see at the top, next to notification bar, you will find a dotted sqaure box which contain folders liek "My Accounts, Search, Map etc". Now see at the bottom, you will find option of more. Click on it. Now there you will find "Hangout" folder. Click on it. Once you click it, a handout page will get opened. Now at the extreme left, you will find "Menu, then at bottom you will find Contact, Conversation, Phone Calls, More". Click on "More". After that at the bottom, you would find "Settings option". Now in that you will find A box like "Share your status" and all. Again go at bottom, you will find "Hidden Contact". Go on it and you will find hidden contacts and now you can unhide whom you want. All the best.