Can the response midi gateway receive midi input over USB?

Response MIDI Gateway can definitely receive MIDI over USB to output on its 5-pin DIN jacks.  I double-checked this with a Response MIDI running 2.2.0.5.

I would suggest having a look at snoize: MIDI Monitor as a piece of software that runs on MAC - it will detect USB-MIDI devices and log the MIDI messages that are coming and going.

A caution - if you are also using ETC Eos software on that same computer, you will want to disable it from using this device - only one software at a time can use a MIDI endpoint.  Depending on your Eos software version, that's probably in Browser > Setup > System Settings > Show Control under the USB MIDI/SMPTE tab.

I assume that it can also output the MTC over a network? 

Yes, Response MIDI can be used to both send and receive MTC. 

To be fair, I've really only tested it with Eos software receiving MTC, so I cannot speak for someone else's application receiving MTC from Response over the network.  Eos software cannot generate MTC, so I've used MIDI-Ox for that, with Response MIDI plugged in via USB to the MIDI-OX computer.

Alright, I got it to receive Midi over USB using my MacBook, I'm not yet sure why it wasn't connecting right with the Mac Pro. One thing: is it supposed to show the midi sent to it over usb as midi out? The response gateway is showing a (y) under the "Out" on the LCD, and if I look in the about menu, I can see the notes I sent it under the Midi out section. Since the gateway is connected to the MTC source via USB, I would assume that the midi being sent to it would be received as an input for the gateway to output over 5-pin midi or network.

This Gateway can send and receive MIDI (notes, MSC, MTC) through its 5-pin DIN connectors as well as through USB, and over network as UDP messages.

So, if it's getting MTC from a computer via USB, it will Output that through its 5-pin connector and also send it over the network (when configured).  Thus, you'll see a (y) under Out.

Edit: MIDI over USB to the Response MIDI Gateway is not forwarded out onto the network.

If another device is putting MTC into a MIDI cable, plugged into the 5-pin IN connector of this device, then it will show a (y) under In and it will pass that MTC up through the USB connection, if made, and on the network, if made.

It's also possible to send MIDI to this device via UDP over a network.  It will then pass that MIDI Out of the 5-pin connector, but will not see it as "input" to the USB side.  

Would looping the 5-pin midi out to the 5-pin midi in cause it to send the same midi across the network?

MTC from Mac to gateway over USB -> Midi out via 5-pin port -> Midi returned through 5-pin input -> midi sent to network

I'll also look Into using UDP.

I just tested the midi loop and it does work

Edit: in my test, the midi was coming back to my laptop over the same USB cable.

I just tested the midi loop and it does work

Edit: in my test, the midi was coming back to my laptop over the same USB cable.

Sample from Midi Monitor:

13:18:27.137 To ETC MIDI (00:c0:16:04:77:0a) MTC Quarter Frame 75
13:18:27.139 From ETC MIDI (00:c0:16:04:77:0a) MTC Quarter Frame 75
13:18:27.145 To ETC MIDI (00:c0:16:04:77:0a) MTC Quarter Frame 80
13:18:27.147 From ETC MIDI (00:c0:16:04:77:0a) MTC Quarter Frame 80

I'm using nomad to receive the timecode for testing purposes, and it seems to have a delay (maybe 10-20 frames) from the midi source to EOS. Is this normal for EOS?

I wouldn't expect a delay of 1/3rd to 2/3rd of a second between MTC sending device and Eos software receiving.  Are you doing this testing using the round-trip loop you described earlier?  

I took a screen capture of MIDI-OX sending MTC over USB to a RSP-MIDI Gateway in 2.2.1, looped back into itself, then on the network for Eos to listen to.  I am seeing, at most, 4 frames difference between these two clocks, but often no difference.  And this is an atypical setup, requiring the MIDI Gateway to be both sender and receiver, with data transiting the USB link and being handled in two different pieces of software inside the same computer (which is also doing lots of other tasks, like capturing video).