I think that both are different in csab all candidates across india can participate but in csab neut only north eastern state and union territory students  can participate There are eight North-Eastern states are involved in CSAB NEUT 2021 includes Arunachal Pradesh, Meghalaya, Assam, Mizoram, Nagaland, Manipur, Sikkim & Tripura. Since both counselling are different so you can participate in both separately but if you are not from neut's then you should participate in csab counselling special round only as it is better for you