DEP Pre Reqs from a Mac OS perspective

I'm not 100% sure but I would make an educated guess that access to Apple (17.0.0.0/8 network) and APNS (since profiles are installed) is required.

You can quickly check which ports are open with Two Canoes Push Diagnostics.

Can anyone confirm if APN's needs to be enabled and configured in order for DEP to work?

Yes.

https://groups.google.com/forum/#!topic/macenterprise/kwANGD-XGGM

To expand on the correct answers given so far:

• DEP's purpose is to enroll devices into an MDM solution.
• MDM requires APNs.

QED: DEP requires APNs