I just tried to launch Weave with Docker Swarm (Version 1.12, RC 2).
That is not working.
According to Weave engineers this is due to that Docker is not supporting plugins in Swarm mode, (Version 1.12). moby/libnetwork#1296 (comment)
However, this leads to the following situation, that weave (and other network plugins) can not be used with Docker swarm after Docker 1.12.
I do not think, that this is a wishful situation for the community. Plugins are really useless then ...