in general yoga in any form is likely to be helpful for constipation.
Whether it counts as your "daily exercise" in terms of aerobic activity that gets your heart rate up and keeps it there, depends on the type of yoga you practice.
Some classes are very slow paced, gentle, and you don't even get up off the floor (like a yin class). Others involve almost continuous flowing motions and activity and you will not only get your heart rate up you'll likely have sweat dripping off your nose onto the floor because it's such a vigorous workout (like an ashtanga or intensive flow class).
You can use yoga for your only exercise if you take classes that count as aerobic, or do something else aerobic and add in yoga for the IBS-specific benefits.