Ray, I have done a little research--not much though--into the question regarding who the Federal officer brother of Tim Reeves was. Speculation has seemed to center on Albert Reeves of Butler County, after whom Reeves Station is named. There was a Private Albert M. Reeves who can be found in Benton County's 60th Enrolled Missouri Militia in 1864, and then the Benton County V.M.M. in the summer of 1865. That could mean that a Union-supporting Albert got the heck out of the no-man's land that was SEMO and headed for friendlier confines, but it doesn't really answer the question of whether this was the Reeves brother being referred to (especially since Benton County Albert was an enlisted man, not an officer, and the timeline does not match up).
And while speculation has focused on Albert (since he is the one brother SEMO historians have the best knowledge of), completely overlooked are Reeves brothers John, William, Terrell and Gaston, all of whom are possibilities. There are a couple of other brothers, but their war-time ages would seem to preclude them.
Someone with a bit of time might cull through the Missouri Secetary of State cards to see if a man with any one of those names appears as an officer in a Federal Missouri unit, including the EMM. If their name appears as an officer in a MSM or U.S. Volunteer unit, then order the military file and/or pension file on that person, if such a file exists, and look through it to see if information in the files overlaps information we have on Tim Reeves. If their name appears as an officer in an EMM unit, or other more localized militia unit, then we may not ever solve the mystery since no files will exist.
And, since we should not focus solely on Missouri units, a search through the units of other Union states could be made to see if any officers appear with the names of Albert, John, William, Terrell or Gaston Reeves. Include Albert, because he is not necessarily eliminated since we don't know whether or not the Benton County enlisted man Albert Reeves is the Albert Reeves who is the brother of Tim Reeves. Anyway, could be that the Federal officer brother of Tim Reeves joined up with one of the number of outside U.S. units that were in Missouri early in the war, or that brother may have crossed the river and joined up with one somewhere else. The Soldiers and Sailors website might be of help in this regard. Just look to see if any of these names crop up as being officers in a U.S. Federal unit. And then order military files and pension files on prospects were officers.