Can creatures with summoning sickness block?
Yes, you can block with a creature affected by summoning sickness.

This is the Comprehensive Rule about "summoning sickness"; I emphasized the relevant parts in your case:


  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 sickness” rule.


As you can see, at no point the rule states that you cannot block with a creature affected by "summoning sickness".