Can Bamboos Be Grafted?

No, bamboos are giant woody stemmed grasses and like any grass it cannot be grafted. When a culm is damaged the wound will cauterize but it will not produce new growth cells that would allow it to grow together.

That being said, occasionally freak growth can be observed that would appear to be grafted. Check out the photo below, it appears that 2 shoots grew together or grew apart. When I found this culm it was already grown so I'm not sure it was the latter or the former.

Notice that the culm begins to separate where the internode length begins to diverge.