At a guess there would be no problem. Otherwise an engineer would not be able to carry out ground runs.
Suspect it is to do with the definition of Flight Time, which if I recall correctly starts from the moment that the aircraft first moves under its own power with the intention of taking off.
Therefore you can log it as flight time even if you don't take off (say a rejected takeoff or a problem on run-up).
If you are not intending to take off it's not flight time, and therefore presumably you don't need a licence.
Otherwise the Guys at Brintingthorpe could be in trouble taxying their Vulcan!
Mike
(ducking back below the parapet
)