In theory yes, they even might be already, it's just that we don't really know what Mou expects from particular players/roles. Narrowing it down to goals/assists due to them being attacking player, albeit logical, is short-sighted I guess. Jose has his reasons to play Mata even if statistically speaking he's produced feck all, just like he has his reasons to I think always take him off around 60-70th minute.
So far I think that the picture is clear that it's Rashford/Martial competing for the left, Miki being #10, Lukaku/Rashford for #9 (no reason to drop the former), right is mostly Mata. Maybe keeping Martial/Rashford sort of pissed off at not starting every game is his plan, to keep them competing and pushing one another? Maybe he knows that they might burn themselves if both play all the matches? Maybe he wants a pacey winger to get onto the pitch on the tired legs so one of them is always going to inevitably sit on the bench, because an impact sub is a very important part of his game plan? Maybe it's the mix of all really.
I don't know if Martial will start against CP, I'm sure that Rashford and Mata will though, both rested against CSKA.