Can creatures with summoning sickness be tapped for convoke?
Yes, they can. You are probably thinking of the "summoning sickness rule", which does not apply here:


  302.6. A creature‘s activated ability with the tap symbol or the untap symbol in its activation cost can‘t
  be activated unless the creature has been under its controller‘s control continuously since his or her
  most recent turn began. A creature can‘t attack unless it has been under its controller‘s control
  continuously since his or her most recent turn began. This rule is informally called the "summoning
  sicknes" rule.


So this rule doesn't prevenet creatures for being tapped for any reason other than paying the activation cost of that creature or attacking with that creature.