Fascinating question!. In addition to the "can it make something nearby fleishig" question, there may be additional issues: If the beef is from an animal that was not slaughtered properly, does that add additional issues? If the candle is made from an animal that is inherently non-kosher (pig, camel, etc.), does that add additional issues? I am fairly certain that if a candle is made from milk + meat that you would not be allowed to use it at all. But in the other circumstances (non-kosher beef, never-kosher other animal) you can benefit from the item, but Kashrus may be an issue. From a physics standpoint, I suspect (but we really need someone with Halachic knowledge for a proper answer) that smoke/soot are a non-issue as they are combustion products and not "remnants". On the other hand, the smell of the candle burning could be an issue, and any splattering of melted tallow would definitely be an issue.