Given the fact that many ghost-types feed on the human soul, they’re among the only pokémon that are very, very bad choices for service pokémon. This includes lampent, who—while not actively aggressive—is an opportunistic pokémon who will feed on a soul as it leaves the body. So on a technical level, lampent is harmless to people who are recovering or in need of day-to-day support, but it’s rather tactless to give them to the terminally ill or elderly.
For those wondering, the other types not particularly recommended for use as service pokémon are bug-types and poison-types. Of these, poison-types may be the most willing to act as service pokémon, but many of them will inadvertently sicken their humans, either because of the toxins in their body or, in the case of the grimer and trubbish lines, because they’re not very sanitary. Bug-types, meanwhile, typically couldn’t care less about the plight of humanity.
The Pokédex According to Bill 