Battlemage is supported as of Unraid 7.1
I have been using it since 7.1 with no issues. (except there not being any good gpu stats plugin)
For anyone using the Linuxserver docker, to get this latest version add/edit two variables:
VERSION=1.43.1.10495-10cfae054
PLEX_DOWNLOAD=https://downloads.plex.tv/plex-media-server-builds
The url has changed since the previous release.