Docker containers start first, then VM's
While the startup selection in the docker page is a plus, considering that a startup order of A,B,C vs a startup order of B,C,A doesn't make a ton of difference since as soon as container B is started, the next in the order is started immediately (the faster the cache drive, the more this is exacerbated all else being equal) . But, B may still be firing up, so any dependencies that A for instance has on B or C may still not be met.
While the docker start manager came out before unRaid's UI supported a startup order, and now they do somewhat overlap, it still has its place as it lets containers either have a set delay before starting, or check to see if such and such port responds on such and such IP before starting. (useful for dependencies against a VM)