On Project Server (or Project Online) 2013 the iPad is about 98% compatible. You should have no problems with an iPad and 2013. On Project Server 2010, it depends a bit on what you are doing. There are apps that make it more easy to use but I am guessing from your question that you are having folks sign in directly with Safari (or other browser). I have used iPad with 2010 but the success of using it depends on exactly what you are trying to do. Some of the basic stuff works and some of the things that you would think would work do not because of various settings in the browser and/or the way the data is reached.