Yes, many children leaving Montessori preschool programs do read. (please note that Montessori's concept is that "preschool" is ages 3 to 6 years old, so then your child would enter 1st grade, but many people do leave after 5 years old and put their children in kindergarten).
However, it's not necessary that a child be reading before kindergarten - not all children do and many children cannot really read until 1st grade. Unfortunately, we've pushed all of this down so there is a real pressure to be reading by the end of kindergarten, which means that we think there is something "wrong" with a child who isn't, when developmentally it's still appropriate to really "get" reading in 1st grade.
I wouldn't worry about your child reading before kindergarten. I would want you to choose a preschool program which has a philosphy you really agree with. So VISI, VISIT, VISIT!