I was playing UEF the other day and when I set and engineer to assist another engineer he doesn't follow through with the command. He will go to the other engineer but will not actually assist. The main engineer usually has a build order queue, then I set all engineers to assist him upon production. Or in the case of a factory making offensive units and I would set all engies produced by factory 2 to assist factory 1. They walk to the factory but do not actually assist.
Though If I select the engie and right click to assist it does work correctly, but set as the rally point from a factory seems to not work.