I believe that the only reason for the many Pokedex entries about misfortune coming to those who see a Mimikyu's true self, often in the form of death or horrific trauma, is the lack of trust between the Mimikyu and the one seeing it.
In all the Pokedex entries, not one mentions the Mimikyu's own trainer seeing it's true form. In Sun, "a scholar," Ultra Moon, "a passing trainer," and in Shield, "a scientist" are the ones who see the Mimikyu's true form.
Also, none of the Pokedex entries make any mention of a Mimikyu showing itself to a human willingly, with all of them seeming to imply the Mimikyu was unconsenting to being viewed. In Sun, that scholar "saw what was under its rag," in Ultra Sun, "if you try to look under its rag, it will resist violently," in Ultra Moon "a gust of wind revealed what hides under this Pokemon's rags," and in Shield, that scientist "peeked under Mimikyu's rags."
All of this combined seems to imply that if a Mimikyu's true form is seen without the Mimikyu's consent is when the listed misfortunes occur to the seer. The lack of entries talking about what would happen if a Mimikyu trusted a human enough to show themself to that human implies that either what happened as a result was insignificant enough to not be noted or that it hasn't happened to a scientist or professor, as many of them are unlikely to truly befriend a Pokemon they're studying.
I believe that the animation that plays after a use of Teleport is meant to symbolise creating a portal. These portals can be used by other beings than just the Teleport user; however, this is illegal to do in the Pokemon League, which is why it's not used like that in battle in the games.
In games with HMs, some other optional moves could be used outside of battle, Teleport and Dig. The fact that Teleport could be used to return to the last used Pokemon Centre proves that other beings can go through Teleport's portals.