Yes.
That said, those who read the DMG to find information they shouldn't have - e.g. what does this item do that our party just found - are IMO flat-out cheating.
I would call players cheating if they broke an established rule that is in place in the game.
A Gm whose table rules forbade reading the DMG would simply see me say "well, bye, i read it long ago." So, there is that.
To me, players can read DMG, PHB MM whatever... though i would ask for them to tell me if they have read any established adventure packs just so we know.
However they all need to know that i change a great many things.
As for knowing "what that magic item we just found is"... The DMG will not help them there much more than it is likely to hurt them in my games.
The day i start hinging any important element or aspect on my game on players being *ignorant* of published material is the day i set aside GMing.