Historically getXbyY functions and the name service switch had a way of doing that, and that was one reason for nscd to come along (another was to cache better, naturally).
Most (all?) of the nsswitch functions were datagram based back in the day, so those would be safe.
I've certainly never had issues using e.g. getpwent on a NIS setup with forking and modern rpcbind may use TCP I believe. Maybe it opens a new connection each time?
