Both Donemana and Clontarf have their overseas professionals for the 2020 season.
Adams has spent one season overseas with that coming in 2015 during a stint at Cherry Tree CC in the Lancashire League where he scored 706 runs at an average of 44.13.
A batting all-rounder, the 30-year-old currently plays for Boland in his homeland and has competed in 37 First Class matches, hitting 1747 runs at an average of 30.12 and high score of 149.
He has also picked up 108 First Class wickets with his pace bowling at an average of 25.31.
Marais will be well-known to Irish cricket supporters after spending both the 2015 and 2016 campaigns with Fox Lodge.
The South African had a lot of success in the North West, scoring 1336 runs at an average of 78 in his first season before following it up with 916 runs and average of 70.46 in 2016.
He joined ECB Southern Premier League side Alton CC for the 2018 season but his time in Hampshire was cut short due to injury, leaving after 12 innings where he scored 393 runs.
The 26-year-old, who plays for Eastern Province, scored the fastest triple century in First Class history back in November 2017 when he reached 300* from 191 balls, which included 35 fours and 13 sixes.
Both players have been placed by agency WSX Cricket.