The Dungeon Master's Guide (p. 258) describes a risk if you badly fail to harvest poison from a creature:
A character can … attempt to harvest poison from a poisonous creature … The creature must be incapacitated or dead, and the harvesting requires 1d6 minutes followed by a DC 20 Intelligence (Nature) check. (Proficiency with the poisoner's kit applies to this check if the character doesn't have proficiency in Nature.) … If the character fails the check by 5 or more, the character is subjected to the creature's poison.
The Tool Proficiencies section of Xanathar's Guide offers advice on how to use tools, including the Handle Poison section of the Poisoner's Kit (p. 83) tool description:
Your proficiency allows you to handle and apply a poison without risk of exposing yourself to its effects.
Would this mean that a character who is proficient with the Poisoner's Kit could happily fail the harvest poison check by 5 or more without being subjected to the creature's poison?