I can't comment on the commonality of aliases, but I can note that my grandfather Herbert C. Thomas enlisted, underage, as Harry Thompson (sic ?). He was apparently only 16 and was eventually discovered. There are two known color pictures of him in his uniform. One was in the possession of John, his son, deceased, and/or John's son Jamie/Jaime, last known to be in Veedersburg, IN, area.
This picture or a copy is very much desired.