Dan has been released from the Scotland squad to play after making a big impression after playing in the second half of Glasgow's 28-28 draw with Connacht last weekend. Sam comes in for international Graeme Beveridge, due to become a father for the first time next week.
"Dan and Sam are both physical players and we will need those qualities against the Dragons," said backs coach. "It's a massive challenge for the boys who played really well in the second half against Connacht after a pretty embarrassing display in the first 40 minutes.
"We've eight games left and our target is to win them all and qualify for next season's Heineken Cup."