No, a bearded dragon cannot eat a millipede at all as they are poisonous towards beardies.
The reason why they are poisonous is that they release a fluid from their butt which contains cyanide in it which would most definitely kill a bearded dragon.
Therefore it is very important that a bearded dragon does not eat a millipede.
In addition the millipedes can possibly be carrying other diseases and parasite which would be harmful to a bearded dragon.
Millipedes consist of different segments of body which all bear two pairs of legs across an elongated body. They are myriapod invertebrates.
They like to live under objects such as stones or logs and in soil as they do not like light.
They are part of the class Diplopoda.
Remember never to let your bearded dragon eat this insect as it is poisonous towards them.