Is it actually true that ciggarettes or smokeless tobacco will show up on a probation drug test?

No: Probation tests involve testing for illicit substances, in which category tobacco does not fall. Unless there was a judicial order that you not smoke, there is little or no likelihood that they would be even testing for cotinine, the metabolite in urine, or care about it. In minors, some juvenile authorities might be interested, since it is not legal to sell cigarettes to people under 18.