gum does need a hechsher. the kashrus agencies (ok, ou, crc) online explain that gums have ingredients in their bases such as glycerin, rosins, etc that are often from animal products. just because you don’t swallow something does not mean it’s not a real food halachically (and thus doesn’t need to be kosher). for a rayah, see o.c. 202:15, which says that you make a beracha if you suck on a sweet stick. aiii, but it’s only sucking (so why make a beracha)? talmud lomar, it doesn’t matter, sucking is considered eating, and thus requires a beracha. So too, the thing being sucked has to be kosher.
Abba_S: are you asking about chewing tobacco? Smoked tobacco does not need a hechser; there is no maaseh achilah and reicha lav milsa hi. tzarich iyun about chewing tobacco- look at the ingredients for a start.