Can dulera (formoterol and mometasone) and ventolin be taken togeter?

Yes. A scenario where one may be needing to take Dulera (formoterol and mometasone) and ventolin around the same time would be during some type of asthma/copd exacerbation. Remember though, Dulera (formoterol and mometasone) has a long acting form of albuterol (the active ingredient in ventolin). So normally, one would not need to take them both at the same time.
Yes. Dulera (formoterol and mometasone) should be your daily maintenance inhaler and ventolin is your rescue inhaler when you get short of breath.