That holes 'must' be filled on broadleaved trees, deciduous or not, is a myth.
True : that reminds me of a programme I saw on Arte, the "story" of an old maple in Britain. David Attenborough. He explained that the inside of the tree was actually dead. I can't find a link to the video.
If the dead part of the trunk, it won't risk to infect or damage the living tissues around, so, yes, deadwood is
a natural feature on some trees.
Then, if done artificially, it must look credible. Walter's Acer campestre is a very good example of that.