I'm taking Zetia plus crestor (rosuvastatin). Is it ok?

OK. This combination is safe as long as you monitor your blood work including liver and muscle enzyme tests. In my experience Crestor (rosuvastatin) is usually very effective so that it usually isn't necessary to add Zetia if you take a large enough dose. Your md will guide you however.
OK. There should not be any significant interactions between these two medications. One thing to consider/discuss with your doctor is what dose of Rosuvastatin you should be on (low dose, eg 10 mg or high dose eg 40 mg) and what additional benefits ezetimibe confers.