Relay is fully open to any NIP-42 client direct. Primary path, already working in Damus, Yakihonne, Coracle today. (Haven't tested Amethyst, no Android handy, would love Vitor's take if he gets a chance.)
The partner credential is for cache-service clients where the app talks to a backend rather than to relays. I tested Primal signed in as a paid subscriber with the gated relay added to my client and still couldn't read the article, which is what got me looking at their architecture. From primal-web-app/src/sockets.tsx the web app opens one websocket to a cacheServer URL and speaks a Primal-specific protocol, no direct-relay reads in that file. Might be wrong about the rest of their stack, but if that shape holds the cache itself is what needs a NIP-42 identity.
For client architectures without that intermediate layer, there's nothing to integrate. Just connect.
https://github.com/PrimalHQ/primal-web-app/blob/main/src/sockets.tsx