there is no special magick for that, I have already seen a (not very clean) network where many PC had a classic network card and a wifi card enabled, both configured with DHCP, and these 2 cards had of course different addresses on the same network.
Now these PC where only clients, obviously, and they accessed the network normally through their default route. From what happened it seems clear that the OS of these computers was always picking the faster link, that is, the Ethernet card. But when people disconnected the Ethernet they could access the network just as well through the Wifi, so the software was redirecting the default route dynamically.
When you have a server, it’s a different thing to have 2 interfaces on the same network.
It can happen but in this case you may have to struggle with some not very standard routing.
When a packet comes in on the default route card, no problem. In the other case, when no special routing is done the reply packet will come out on the default route card. I tried the setup and netplan (i think that the culprit is netplan) is creating 2 default routes :-(. Ugh. Ping works for me., but I did not try a TCP connection, it may very well be a blocker in this case (since ping is connection-less possibly the route problem is probably irrelevant)
So I’m 99% sure it’s not a LXD specific problem.