No in everyday colloquial speech, they are often wrongly used interchangeablly, but technically and for the dictionary definitions they are not the same. Dominant = to have power and control over someone, "she spent years with a dominant husband, who would not let here lead a normal healthy life. After years of verbal and emotional abuse she finally filled for divorce" PREdominant = the main and overriding feature in a room (in your context) is the fireplace. "The predominant feature of my clients marriage your honour was her husbands dominance over her" so for your sentence for passing exams it should technically be the predominant feature of the room. for colloquial speaking you will not be questioned.