The Ireland international, who represented Salford at scholarship level, could come straight in for his debut against Leeds Rhinos on Saturday.
Roberts has been struggling for game-time at Huddersfield and is yet to feature this term.
“I’m really looking forward to getting stuck in with the boys,” he said.
“I know quite a few of them and they say really good things about Ian Watson.
“I like his style of play and I think it’ll suit me quite well. That was one of the main reasons I decided to come here.
“I want to have a good impact from my first game and bring something to the team. Give them a bit of a boost.”
The 25-year-old will link up with fellow Giants loanee Sebastine Ikahihifo in the Red Devils pack.
Head coach Watson said: “Oliver’s a player who I’ve admired for a long time.
“He really impressed for Huddersfield and in the World Cup and then it looked like he would kick on from there.
“We want to give him a place where he can play to his strengths. He’s a big athletic guy, with leg speed and the ability to bust tackles and offload.
“He’ll definitely bring a massive strength to our attacking game and defensively, his understanding means he’ll add competition across the board.
“He’s got a point to prove, like Seb did, and if he starts the same way then it’s been a great signing, because Seb’s been outstanding for us.
“It’s really important that we’ve been able to bring someone of this calibre in at this stage and that makes everyone who’s been backing the squad builder scheme invaluable.
“Hopefully, going forward we can look to bring in some more quality players, with the increased support and more people becoming squad builders adding to our resources.”