It does Serf over UDP, but I get fuzzy on the integration of Serf and Consul.

Raft and the Consul RPC API use TCP, Serf uses both TCP and UDP.

While the Consul RCP API may have grown options to use GRPC (I forget now), Raft uses length-prefixed msgpack PDUs.

Whoops, I thought this was a Google product, given the discussion. Stubby is basically GRPC internal to Google.