Just to make this as an answer and also to answer your edit:
Check your Folder Options.
[x]Hide Protected System Files is ALWAYS on by default. And hiberfil.sys is one of that protected system files.
Once you untick that, there are lots of system-protected hidden files you can see. So yes it CAN be visible, if you have a reason why you need to find it.
In response to your edit:
dir /a *.sys
will return a result as /a means it will ignore whatever File Attributes (hidden in this case) that was set and return the result to you.
Not visible in explorer is normal (again will be visible after you unhide protected system files).
If you want to delete hiberfil.sys simply turn off your Hibernate function on windows. One easy way is to open command prompt (as administrator), and type
powercfg -h off
It will turn off the Hibernate function of your computer, and also automatically delete the hiberfil.sys file. If you actually DO need hibernate function (mostly for laptop, not so much for PC), you can turn it on again by changing
on with the above command.