According to http://build.mctcp.com/job/TerrainControl%20-%20Master%20-%20Gradle/ the last two builds failed, one of them shows 1.11 compatibility, but a dev doesn't seem to have addressed whatever has caused them to fail and that was last month so are they safe to use for world generation on Bukkit/Spigot?

Thanks

I Doubt it. Because the Succesfull builds are all 2MB in Size, while the two Failed builds are only a few Kb in size.

I assume a Failed build on the BuildServer means the Compilation somewhere crashed/failed and isn Completed.

Build server is fixed by now. Take a look at this wiki page to see which build is best for you.