Knowing Alex Smith I doubt very much he would have advised Clarke, or anyone for that matter, not to sign for Rangers. And certainly not for religious reasons.
Souness has spoken many times about trying to sign his first catholic player.
Never once has he mentioned Steve Clarke as that guy. He's mentioned the likes of Houghton and John Collins but never him.
Davie Hay tried to sign him for Celtic but I'm skeptical as hell that Souness tried to sign him for us.