Correct, according to Danish law, it is a blunt weapon and you should have evidence that he has a blunt weapon collectors license before posting it. He can apply for this online and it takes a couple of months to process.
It would be easier for someone coming to an event here, such as Moesgård, to bring it out as the organisers will have arranged temporary permission for guests to carry blunt weapons and to use them. However, he will still need the full license in the medium term.
Please also remind him that to use blunt weapons for reenactment/living history/HEMA in Denmark, he will need another license for each and every weapon, and that means that he must be a member of a recognised group. The police do check, but if he is with a good group, they should have helped him with this already.
Feel free to point him my way if he is looking to discuss viking stuff in Denmark