Can a reservoir host act as a vector?
A reservoir host most obviously is a long-term carrier organism of a given pathogen that doesn't exhibit the disease caused by the pathogen.

A vector is literally any agent that transfers the pathogen to another organism. If you think about it, a reservoir doesn't have to be a vector i.e. there's no route of transmission they participate in, but a vector can certainly be a reservoir, such as bats, who often act as a vector for the pathogens they house (think Rabies). On the flip side, ticks are common vectors for Lyme disease, but small rodents actually act as the reservoir for B. burgdorferi (1).