Yes biking is a good form of cardio for anybody. I tend to take long bike rides at night for about 3-4 miles a day. I burn a lot of calories while doing it which is helping me with losing weight.
I love riding the bike, but prefer running, as I feel more muscles are used while running. Especially more muscles in my belly
Myself not a runner but I use an exercise bike a couple times a week, usually about half hour each time. If running works for you fine. Not for me though. I am planning on a regular mountain bike this spring or summer. I find the exercise bike gets a bit boring and might enjoy it a bit more actually going outside. Ryder13
Don't know about bodybuilders but some guys who workout at my gym, who are pretty big, that bike a lot. They usually ride this trail that has a lot of hills. They say it's the best trail for riding bikes and being in shape.
