It's hard to say about Sceviour, it's been apparent the coaching staff does like veterans in those roles more often than rookies/younger players, I think Sceviour was just a throw in to balance the cap hits (somewhat) while also finding use for him as a ZAR injury replacement on the 4th line, he's just a safe 4th line player, nothing more, nothing less. A known commodity over an unknown that you'd be trying to figure out (I would have rather seen Lafferty used instead).
As for Matheson, all I can do is read about him and I'm not a fan, but I can see the potential if he does work out, but it's quite the gamble on a pretty ugly contract if it indeed doesn't work out.