[RyanN]

No, you must use the OI's power if you wish to power anything. The only exception is the chicklet.
I change my opinion after closely reading the manual. You can connect LEDs as long as they do not connect to the joystick ports:

<R105> All equipment connected to the joystick ports of the Operator Interface must be powered
solely through the power available through the port. External power sources of any type are
not permitted on any equipment connected to the joystick ports. Portable computing devices
must not be connected to joystick input ports on the Operator Interface. Power-passive
devices (e.g. joysticks that draw their power solely through the Operator Interface joystick
port) are permitted.
<R106> Devices connected to the joystick ports of the Operator Interface via a FIRST-approved
USB adapter (the only approved USB adapter is IFI Part Number USB-CHICKLET) are
excluded from Rule <R105>. If used, this USB adapter must be powered with a 7.2V battery
functionally identical to the back-up battery. Power from the competition port or any other
source shall not be used to power the USB adapter. The USB adapter must be positioned
within the OPERATOR CONS