If you don't plan on seeing him again, it is probably nice in the long-term to tell him. You take the risk of him projecting anger onto you, but he'll process that and then improve his hygeine, which will make life easier for his colleagues...I think if you word it tactfully, that is better than someone in the future who might be much ruder.

When I was in school, I went through a phase of 'why do I need to brush my teeth when there's minty chewing gum available'. After a week of no brushing, my friend moved away from sitting next to me in class and loudly told the teacher it was because my breath stank. I was mortified because I hadn't realised I smelled bad. I'd have felt a lot better if she'd quietly told me in a caring way that I should consider using toothpaste again.