Often times, yes. You could also high poly model it in Maya or another standard 3d app if it's easier. Kinda depends on what the object is and what tool is best for the job.
By the looks of it, it is completely modelled in maya or max using sub-d modelling. For a fire hydrant like this, i wouldn't use zbrush or mudbox other then for details like scratches and dents.
one workflow would be to block out your mesh for proportions and size and the like, then if possible use that blockout to construct your high poly, and also as a base for your lowpoly. mileage may vary, of course
^-That's what I mostly tend to do. It really helps you get those first forms for the lowpoly right.
You also got to remember that if you decide to work with zbrush or mudbox, don't do all your models just because you can. A lot of times it is more sufficient to do a proper highpoly, in subD or what ever it might be, and then ad scratches and stuff in crazybump. If that takes you lets say 10 minutes and that pass in zbrush would have taken 1 hour - and they both pass of as "good", then I would go with crazybump. Just saying
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Here's an example of a highpoly fire hydrant with clean geometry (just googled it up as well):
http://th01.deviantart.net/fs71/PRE/i/2010/180/b/5/Fire_Hydrant___Highpoly_by_JeremiahBigley.jpg
By the looks of it, it is completely modelled in maya or max using sub-d modelling. For a fire hydrant like this, i wouldn't use zbrush or mudbox other then for details like scratches and dents.
You also got to remember that if you decide to work with zbrush or mudbox, don't do all your models just because you can. A lot of times it is more sufficient to do a proper highpoly, in subD or what ever it might be, and then ad scratches and stuff in crazybump. If that takes you lets say 10 minutes and that pass in zbrush would have taken 1 hour - and they both pass of as "good", then I would go with crazybump. Just saying