The wording is '1. An airbag obviously missing or defective.' so that's still a fail even if you don't have a light for '2. A Supplementary Restraint System (SRS) malfunction indicator lamp indicating a system malfunction.'
However, there's also a clause that states:
Modified Vehicles
Where a vehicle has been
extensively modified or converted, certain Reasons for Rejection, such as for components ‘missing where fitted as standard’ should not be applied,
for example:
a car converted for rally use (i.e. rear seats removed and fitted with a roll cage and full harness seat belts etc.) may have been converted so as not to require a brake servo, power steering or airbags
a car converted to a stretch limousine may no longer be fitted with curtain airbags or functional Electronic Stability Control.
So you can always argue the point...