Both kinds of herpes can be spread to the other region between outbreaks - it's called viral shedding. Even when there's not an active outbreak, the affected tissue can still release virus.
http://www.goaskalice.columbia.edu/1071.html
It's virtually impossible to tell when asymptomatic shedding is happening, but the going theory is that suppressive therapy (drugs like valtrex or supplements like l-lysine) not only suppress outbreaks but also suppress viral shedding. However, it's not 100% proven to eliminate all shedding, so proceed with educated caution.