The feat "Pole Master" allows you to use hafted reach weapons as Monk Weapons for the purpose of Flurry of Blows. Many if not all of these are weapons that a monk is not usually proficient with. However, the feat itself states that
Your monastic training included extensive work with pole arms.
Now my question is: Does a Monk automatically become proficient with a weapon as soon as it is considered a Monk weapon?
Best Answer
No
"Special monk weapons" are weapons that can be used in a flurry of blows. In core, this includes the kama, nunchaku, quarterstaff, sai, shuriken, and siangham. A monk is proficient with each of these, but they are not proficient because they're special monk weapons—they're proficient because their Weapons and Armor Proficiency section said so. There are quite a few options (particularly in Eberron) that allow you to use other weapons as special monk weapons, but they do not tend to add proficiency either (instead, they generally require it).
The Pole Master feat is, overall, poorly-written. Its wording is vague, but its prerequisites list "Weapon Focus (with a specific hafted reach weapon)," a feat that itself requires proficiency with said specific hafted reach weapon. This means that you will almost* always be proficient in at least one such weapon if you have this feat.
*It's possible you might get this from a source that lets you ignore prerequisites, but I can't think of any.