I am attempting to flash a custom image created with a .bin file to an onion omega 2 pro device and is following https://docs.onion.io/omega2-docs/Firmware-Flashing-from-USB-storage.html. However, I do not have a Dock to look for the USB-to-Serial Device.

Are there special instructions for how to flash a custom image for Omega Onion 2 Pro?

Thank you!

In any case, using the bootloader isn't the only way to flash firmware images to the device. You can do it from Linux as well by copying/downloading the firmware image to the Omega's tmp storage.

See this documentation article: http://docs.onion.io/omega2-docs/manual-firmware-installation.html
In your case, step 1 will be different as you are installing your own firmware, but the rest of the steps should be the same.

You can check out this documentation article for ideas on how to transfer files over the local network to your Omega2: http://docs.onion.io/omega2-docs/transferring-files.html
Just make sure to move your firmware images to the /tmp directory