In theory, 2 centres should work as well as regular main speakers. Of course sound quality will depend on the speakers. There are a number of regular speakers using a centre positioned tweeter (Linn Ninka, JML utopia mini come to mind), so that shouldn't be an issue. And, depending on the model, it is usually voiced to match the regular mains (ie., sound the same).
But, as always, you have to listen for yourself and decide.
But, as always, you have to listen for yourself and decide.