Indrik Umbra does not give any creature the ability to block the enchanted creature. It just forces those creatures which are already able to block that creature to do so.

If, during a player's declare blockers step, a creature is tapped or it's affected by a spell or ability that says it can't block, then it doesn't block. If there's a cost associated with having a creature block, its controller isn't forced to pay that cost. The creature doesn't have to block.