Can Dimensional Barrier be used on Link monsters?
No you cannot use Dimensional Barrier on link monsters as this is the current text.


  Call one monster type (Ritual, Xyz, Synchro, Pendulum, Fusion) For the
  rest of this turn neither player can summon that kind of monster. And
  any monster of that type already on the field have their effects
  negated.


Because it explicitly mentions monster card types, only the mentioned ones can be used. If the card didn’t explicitly mention certain types then you could have used it on link monsters (so taking out the part in brackets). So currently you cannot use dimensional Barrier on link monsters, unless Konami give the card an errata (rewording the card text). 

Please see this reddit page for more information.