We are evaluating ePMP elavate but have found that PPPoE settings are not carried across.
Since there is neither dhcp nor static on the WAN of a PPPoE enabled UBNT device we find ourselves locked out and only able to access the device via the LAN IP (which as previously noted now has no dhcp server enabled) which will require a callout to client site!
We use PPPoE on UBNT CPEs accross our network so this is a show stopper!
We had the same situation (all our UBNT customers are managed through the PPPoE IP), but there are ways to work around it.
First off, we're using the separate wireless management interface feature on our ePMP SMs now, so we don't need to rely on the PPPoE IP for management anymore (which has the main advantage of letting us always access the CPE, even if it doesn't have a valid PPPoE username/password), so we already have an active DHCP server on all of our ePMP APs, which simplifies the process, but you could also just use static IPs, if you don't have (or want) a DHCP server setup on the AP.
Before installing the ePMP software, I just switch the UBNT radio into bridge mode, and set it to get an address from DHCP (alternatively, if you don't have a DHCP server, just set it to a static IP that you'll be able to access), this will obviously break the customer's internet access, but that isn't important, since this is only going to be used during the upgrade process. You could also leave it in router mode, and just change the WAN address to DHCP (or a static IP), but I prefer to use the simplest settings possible, since some of this stuff is carried through to the ePMP settings. After the radio comes back up as an ePMP, it will come up on the same IP you configured (or get an IP from DHCP), and you can then configure the correct settings - I find it easiest to restore a template config and then just set anything that's unique to the customer (like pppoe username/password) afterwards.
It does take a few steps and a bit of time to go through the whole process, but there are certainly ways to make it work and it's still a lot more effecient than a truck roll to replace every radio we have out there.