I'm not really sure what efforts human rights groups have made to go in there. You can, for example, go to some of these areas and camps only if you get governmental permission, which takes some time and some connections. Some journalists can get in. It's a hit-and-miss situation. I would suspect it's more difficult for human rights groups and even for the humanitarian organizations.
For example, MSF was delivering some medical assistance. I don't know all the details of this, but this is how it was told to me. They were ordered out of Rakhine State; then they negotiated with the government to go back into Rakhine State, but in the Rohingya areas, they were told they could only deliver assistance to non-Rohingya. Their decision was that if they were going to be restricted in that way, then they were not going in. That's why they are not able to deliver assistance within those camps.
Access is very difficult and controlled. There are checkpoints everywhere. This is only complicated by the fact that there is still armed conflict in Rakhine State between the Burmese military and the Arakan Army, for example.