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"Unlike mundane armor, mage armor entails no armor check penalty, arcane spell failure chance, or speed reduction."
This tells us that the Mage Armor is armor... but it also tells us that the armor is completely non-hindering. Thus it should not cancel out any abilities, even ones that are canceled for wearing armor.
"An invisible but tangible field of force surrounds the subject of a mage armor spell,"
This part tells us that while it is armor it isn't really like armor, as it is just a field of energy. Further enforcing it's non-hindering nature.
Remember also that if you deny Mage Armor from working on a monk then Bracers of Armor also would not work.
mage armor is fine for monks as is the shield spell
The Shield and Mage Armor spells were invented for exactly this purpose: so people who can't wear armor or use shields can have armor and shield protection.
In Pathfinder Society, it is considered common courtesy for the party Wizard to offer Mage Armor to the party Monk.
In Pathfinder Society, it is considered common courtesy for the party Wizard to
offer Mage Armor touse the Monk's wand of mage armor on the party Monk.
In all seriousness, buying a wand of mage armor is pretty important for a monk in PFS. Especially at low levels. It means the caster doesn't have to give one of his precious spell slots. Even at the higher levels you still might end up in a party where someone can use the wand but no one knows the spell.
As an aside, if you look at some of the first Adventure Path books (the ones with pregenerated characters in them), Sajan (the iconic monk) uses bracers of armor while keeping his monk AC bonus.