Just to be clear. I assume that you are pointing to the Power Output table in the spec. The roboRIO User Manual talks about a 5.0V rail and block diaghram shows the onboard DIO, MPX, SPI, and AI using 5.0V. Is the 1 A of 5.0V from the table the total that is available for all 5.0 V functions?
Yes. The user 5 V rail is all shared across all places you see reference to 5 V (such as AI, DIO, SPI, etc.). Other integrated places where 5 V happen to be used are not included such as USB vbus. You can read the current and voltage of the user rail in the power API of WPILib.