hybrid for aerobics?

Hi,

I want to do less running and start biking. Hopefully it is gentler
on my legs. I am considering a hybrid instead of a road bike. I will
use the bike for city commuting, and I do not think a road bike is good
for this. And I do not like riding with drop bars.

In aftertoons and weekends, I would like to ride on dirt roads outside
the city. My question is, is a hybrid good for aerobic exercise?

Thanks,

Kang