The experienced Wales duo will provide a welcome boost to a Blues pack which too often found itself under severe pressure at the set-piece last term.
Rugby director Phil Davies has also given youth its chance by offering professional deals to Wales Under-20s captain Ellis Jenkins and team-mate Thomas Pascoe.
The pair were part of the squad which lost out to England in last weekend's IRB World Junior Championship final.
Ben Roach, Aled Summerhill, Will Thomas and Miles Normandale are the other youngsters to be given a chance, while Sevens international Richard Smith is also handed a contract.
The most high-profile departure is that of Wales and Lions centre Jamie Roberts to French Top 14 side Racing Metro, with fly-halves Ceri Sweeney and Jason Tovey, plus wing Tom James and prop Campese Ma'afu also heading through the exit door.
Former New Zealand number eight Xavier Rush has left the coaching set-up, with Dale McIntosh, Andi Kyriacou and Mark Ring all being added to the staff.
Davies said: "I'm hugely excited by the new arrivals, from the experienced Gethin Jenkins and Matthew Rees to the youngsters we have coming through.
"Players like Ellis Jenkins, Tom Pascoe, Ben Roach, Aled Summerhill, Will Thomas and Richard Smith who have all come through our pathway. They are exciting youngsters who I look forward to working with them as we continue to develop."