There have been various popular Roblox games that make use of bioweapons and radioactive compounds. If i’m not mistaken tear gas works in a similar fashion, with dangerous chemicals causing harm to those exposed to it.
Unless the tear gas is used in some sort of self-harming way, which I doubt, it functions as any other weapon would; and if guns, swords, and other “bloodless” methods of hurting/harming others in games are allowed, tear gas fits that criteria.