https://dl.ui.com/firmwares/edgemax/v2.0.x/GPL.ER-e300.v2.0....
All you have to do is click on "GPL Archive" on the download page for the firmware.
I wanted to download the archive for Unifi nanoHD, the GPL archive is mentioned in the download blurb, but there's no link to it and the normal download shows classic proprietary EULA, including no reverse engineering.
They seem to be skirting their requirements in not providing the full git repository for the GPL portions which might be a bit of a gray area but AFAIK the GPLv2 stipulates "The source code for a work means the preferred form of the work for making modifications to it." which I would think would encompass the git repo as well but IANAL.
In the past they also refused to provide the source code for their modified version of uboot claiming some nebulous security reasons but that stopped a little while back.
> c. i. Certain software included in, distributed with or downloaded in connection with the Software may comprise third party proprietary software products that are subject to separate license terms (“Third Party Software”). All such Third Party Software may include software or software components that are derived, in whole or in part, from software that is distributed as free software, open source software or under similar licensing or distribution models (“Open Source Software,” together with Third Party Software, “External Software”).
> c. ii. Your use of External Software is subject in all cases to the applicable licenses from the External Software provider, which shall take precedence over the rights and restrictions granted in this EULA solely with respect to such External Software.
So they've just bundled the GPL software along with the not, and you can freely use the GPL'd software within the context of what the GPL allows.