Gregg started his professional career with the
Spokane Indians of the
Northwestern League in 1910. In 1910, he played for the
Portland Beavers of the
Pacific Coast League (PCL). He threw 14
shutouts with the Beavers. The next year, Gregg played for the
Cleveland Naps of the
American League, pitching to a 23–7
win–loss record with a league-leading 1.80
earned run average. He developed a sore arm in 1914 and had continual arm problems for the rest of his career. He played for them on both the
1915, and
1916 World Series championship teams, Gregg went 9–14 in 30 games with a 3.12 ERA for the last-place Athletics in 1918. When the United States entered World War I in 1918, major league baseball was suspended. At age 33, Vean was too old to enlist. Instead, he went to work the ranch in Conjuring Creek, Alberta, Canada that he had purchased near Edmonton in 1912. He also played baseball for a number of different teams; aside from the Conjuring Creek team, he also played for the Calgary
Great War Veterans Association (GWVA) team in 1919, and was reportedly signed to the Edmonton Eskimos baseball team in August 1921. However, the need to pay off his farming debts pushed him back south of the border. Gregg returned to professional baseball in 1922 with the
Seattle Indians of the PCL and played there until 1924. After the 1924 season, Seattle sold Gregg to the
Washington Senators of the American League for three players and cash considerations. In the 1925 season, Gregg went 2–2 with two
saves. His final appearance, at any level, was in 1927 and consisted of a one-third inning outing for the
Sacramento Senators of the PCL. ==Career statistics==