Is there a law or recommendation to slaughter into a hole in order the blood will go inside, against ghost etc.? I saw it practised in some places (see here an example) but I'm looking for sources or information about it.
Blood of a slaughtered animal is unclean (6:145). It can be disposed of in any way. People will sometimes bury it or wash it into sewage drains. It can be left as such, the issue is not 'ghosts' rather it can contaminate what it contacts and will attract pests, and frighten other animals etc.