Niasse, 26, joins on loan until the end of the current campaign after failing to get a game for Everton this season. He has started only twice since his 13.5 million pound ($16.5 million) arrival at the club last January.
Evandro, who has signed a 2-1/2 year deal, is reunited with new Hull manager Marco Silva for whom he played during his time at Portuguese club Estoril.
The 30-year-old has found himself out of favour at Porto this season. Evandro joined Porto in 2014 and made 58 appearances for the club, 11 of which came in the Champions League, scoring eight goals.
Silva said on Tuesday that the club will need to strengthen the squad if they are to survive the relegation battle this season.
Norway international Henriksen suffered the shoulder injury during the 2-0 defeat by Manchester United in the first leg of their League Cup semi-final on Tuesday.
Henriksen, who is on loan from Dutch side AZ Alkmaar, has made 16 appearances for Hull in all competitions this season.
(Reporting by Hardik Vyas in Bengaluru; Editing by Keith Weir)
