Could just be a simple connection issue - these buckles have a signal wire that runs into them - the connection is normally open until the seat buckle is shived in there and it closes the circuit. You can actually see the wire running out the end of the seat belt anchor point as it runs to the chassis. Not uncommon, as the connection end can get frayed over time or just plain corrode.
I would not disable/disconnect the lamp - as it is also connected to the SRS system which includes the airbag and seltbelt pretensioners. I\'d get it fixed before I\'d try and circumvent any safety system.