What are the effects of "Taint" tokens in Defenders of the Realm?
Yes, they also serve to mark that location as tainted. This is important for the action Heal the Land, or for Inns (which cannot be tainted).
From the Rules:

Heal the Land: If the hero is on a tainted location, discard a Hero Card that matches the location color and roll 2 dice. If a 5 or more is rolled on either die, the hero removes 1 Tainted Crystal from that location. Only 1 Tainted Crystal may be removed per action.
Inns may not be overrun or tainted.