R.E. Hillebrand played one game in the majors in 1902.
At the time, there were a couple Hillebrands in the minors. One, Arthur Hillebrand, went 20-5 for Flandreau. The other, Homer Hillebrand, his brother, was a catcher at Flandreau and came to the majors in 1905 primarily as a pitcher. There was also a Fred Hildebrand who played in the outfield for Lansing in 1902 and an outfielder known only as Hildebrand who played for Ottumwa in 1906. George Hildebrand was in the majors briefly in 1902. There was also a brother of Arthur and Homer named Clarence Hillebrand who played at Princeton University in 1902.
The Wikipedia entry on R. E. Hillebrand (as of 07/27/19) quotes a Chicago newspaper which says Hillebrand was not his real name. However, the other person mentioned in the quote below (Hughes) seems to have been Joe Hughes, so that name wasn't made up.
"A youth named Hillebrand was tried at Pittsburg Friday, but after all was over he was told that while he had done no real hurt he need not stay." - Sporting Life's Chicago correspondent in the Sept. 6, 1902 issue
"Frank Selee had a broken up team here. He tried two lads in right field. One posed as Hillebrand and the other as Hughes. One is said to be Bob Lowe's brother in law." - the perspective of Sporting Life's Pittsburgh correspondent in the Sept. 6, 1902 issue