i personally think the cleaner way would be to ship
/lib/<arch triplet>/libnss_mdns4_minimal.so.2 inside core/core18 and fix the missing bit in nsswitch.conf of the core/core18 snaps:
$ grep hosts /etc/nsswitch.conf
hosts: files mdns4_minimal [NOTFOUND=return] dns
$ grep hosts /snap/core/current/etc/nsswitch.conf
hosts: files dns myhostname
that way we wouldnt rely on the host having mdns (or any workarounds like nscd/unscd) available