De Los Santos, a native of the Dominican Republic, has appeared in six games in relief for Oakland this season and posted a 3.00 ERA, walking three and striking out three over three innings. He was sent to AAA by the A's at the end of April after three consecutive outings where he failed to record an out.
Things got worse for him in AAA after his demotion: De Los Santos has appeared in 28 games for Sacramento in the Pacific Coast League and has a 7.25 ERA over 36 innings. He's striking out 10.8 batters per nine but walking four in AAA.
If nothing else, De Los Santos throws hard. In his limited MLB work he's shown a mid-90's fastball, a slider and an infrequently-used changeup. He has just 36.1 major league innings, so it doesn't make much sense to look deeper than that.
The Brewers will likely send De Los Santos to the minors once this deal is official.