To be honest I haven't had any dealings with a dominator but I find it very hard to believe any decent carb guy can't get one to idle just as good as any other carb. IMO whoever told you that isn't much of a carb guy/tuner.
It's very possible they don't take as much timing as older less efficient engines but I'd bet your leaving some power and road manners on the table with a wimpy timing curve like that.