No, it does not. To connect an external controller you would need to connect via standard 5-pin MIDI or through a computer via USB.

Do the physical MIDI IN/OUT sockets get disabled (like MOX/F) when you connect MONTAGE via USB?

I was (am) expecting MONTAGE, as Yamaha's latest and leading edge product, being capable of acting as a USB host. It makes sense as much as having 5pin MIDI ports. Not every midi controller has 5pin port these days.

The Montage has a "MIDI controller" keyboard and QWERTY keyboard built-in.

Do the physical MIDI IN/OUT sockets get disabled (like MOX/F) when you connect MONTAGE via USB?

On the MOXF the MIDI IN/OUT ports are not disabled when you connect the instrument to a computer. You are misinformed.

Please correct me if I'm wrong but a midi controller is not necessarily made out of keys, can be something like this:
Korg nano pad 2
That requires USB. If it's the case, it's very unfortunate, because what's the difference between a USB host and the 5pin MIDI IN/OUT?! They both do the same thing.

When I connect MOX to the USB port, no signal will be transferred through physical 5pin MIDI IN/OUT and will be routed through the USB port. I should manually go in the menu and choose the MIDI mode so that I can use my controller directly with MOX. I mean I can't simultaneously use both USB MIDI and 5pin MIDI.

Does MONTAGE behave the same?

When I connect MOX to the USB port, no signal will be transferred through physical 5pin MIDI IN/OUT and will be routed through the USB port. I should manually go in the menu and choose the MIDI mode so that I can use my controller directly with MOX. I mean I can't simultaneously use both USB MIDI and 5pin MIDI

What you said was "the MIDI sockets are disabled" which is simply not true. They may not work the way you think but they are certainly not disabled, the MOX, the MOXF, the Motif-series and the Montage all feature a built-in MIDI interface. You can connect a MIDI device to the 5-pin Ports and the Yamaha synth acts as a MIDI interface for the connected device.

They are not disabled. Quite the contrary. They allow the keyboardist to connect an external device through the synth so that either device or both devices can be the controller in your computer-based system. You use your software to accomplish this routing.

Sorry, no you cannot connect your Nano Pad *directly* to the Yamaha synth while the synth is connected USB to a computer. If it does not have 5-pin MIDI ports then connect it to the computer and use your software to merge the signals.

For example, if your "controller" only has USB, connect it to an available port on your computer, connect your MOX via USB to the computer, software like Cubase allow you set both devices as MIDI INPUT SOURCES. Set Local Control = Off on the synth, either device will can be an input source.

It is advanced routing using the computer, but that's how it's done. Trust me.

The fact that USB is a multiple port connection makes it quite different from the 5-pin connection (which is the definition of a single port connection).

By setting you Yamaha synth to USB you must connect it to a computer... The MOX has 5 MIDI ports via USB:
Port 1 is the MOX IN/OUT
Port 2 is for Remote Controlling Cubase/Sonar/Digital Performer/Logic
Port 3 is those 5-pin ports on the back panel
Port 4 is for the MOX Editor VST
Port 5 is for controlling the VSTi template Editor

In Cubase you would set both the MOX port, and your Nano Pad USB port as your "In 'All Midi Inputs'
Now either device can be used to control the MOX, the MOXF, the Motif XF, or the Montage... They all work in a similar fashion.

So the USB connection and the Midi connection can be used, even though your device doesn't have 5-pin MIDI jacks.

If you are not using a computer, contact the makers of the pad and find out what they recommend to connect it.