If you have something to say there is nothing wrong with commenting anywhere. Just know that many hubbers have comments set for their approval before appearing on the hub, so if you don't see it right away that is why.
If they don't answer, chances are they aren't active, so check MY ACTIVITY and if they have no activity showing, they have been gone at least 3 months and possibly longer. You can check the dates on hubs to see last published and that is another way to see when they were here last
If you are following same hubbers, and are looking for feedback, again, probably better off following ACTIVE hubbers, so you get good feedback and possible followers back.
When we talked the other day, I mentioned checking MY ACTIVITY on hubbers you are interested in, so it is a good idea before you waste a lot of time on people who haven't been here from 3 months to as long as 5 years, their stuff is still here, because they didn't close their accounts, but chances are they have gone on to other sites.