Rules? Ironically, "street photography" was born with many people doing work that broke what seemed to be rules. Now it seems to be a self-limiting pigeonhole for a lot of people. I recall an article years back by a former street photog who described a feeling of being a "visual athlete" limited to "making better and better catches" by being stuck in the genre...
Why not use a telephoto if it's what you want to do, so long as you know what you're going for and why you're doing it? Yeah, I had to talk many basic photo students out of buying longer lenses and forcing them to engage with a subject for years. But I'm sure there's very interesting work that could be done on the street by breaking out of the Bill Klein in-your-face treatment, specifically exploiting the aesthetics and characteristics of a long lens. Certainly seems to be a way to do it as a self-conscious exploration of surveillance/anonimity/immersion/identity in an urban environment. Kind of an inverse Friedlander thing, maybe...picking an individual out of the fabric of things rather than integrating him into a complex, layered environment. Dunno; it's not something I'd do, but I can't imagine there's no one out there who could make it work.
Using a long lens as a substitute when you'd really *prefer* to be closer up isn't the way to do it, though. Magnification is no substitute for proximity, if proximity (and intimacy, in the sense of integration/identification with the subject rather than intrusion on it from afar) is what you want.
Edit: And my opinion is that the photos referenced in the original post aren't particularly interesting to me...they do really seem like he wants to be closer, but just isn't.