Vieira was the eighth-ranked Mariners prospect according to MLBPipeline.com who they give him an 80-grade fastball on the scouting scale. Based on reports, his fastball sits between 97 to 100 mph and has reached 102 mph. His second pitch is a curveball that rates above average.
Splitting most of his time between AA and AAA, Vieira in 2017 pitched 54 innings with a 4.00 ERA striking out 46 and walking 22. He did appear in one MLB game against the Baltimore Orioles on August 14th pitching a scoreless inning. One thing that jumps off Vieira's stat page is his ability to limit home runs. In 290 career MiLB innings, Vieira has only allowed 10 home runs and never more than two in a single season. He also participated in the Futures Game this past All-Star break pitching for the World Team.
On the surface, this looks like a good use of the White Sox limited international pool money after signing Luis Robert. With many bullpen openings available, Vieira can fill one of those roles and provides manager Rick Renteria a high-velocity arm to start 2018.
For Seattle, the additional pool money aids them in their quest to sign Shohei Ohtani, who MLBPA has announced they will make a final decision on his availability to sign with MLB club on Monday, November 20th.