You can only wish for unit types, not for specific named units. So you can wish for "Visitor" and expect to get this guy:
Visitor or you can wish for
Man Eater or
Pharmakeia and expect to get the corresponding heroes; and in case they're unique like the Visitor, you'll steal them away from your opponents (teleport to your lab).
But you can't use their names. The thing in brackets is Wiki-specific to distinguish units that share the same unit name from each other, because I didn't want to list them all on a single page but that each one gets his own page - otherwise the "Hero" page would have almost a dozen entries with units that have the "Hero" unit type.
What the game does is compare the thing you entered with the unit type of all units in the game, ordered by unit ID. You'll get the first match, which is why wishing for "Grigori" gives you this guy:
http://dom3.servegame.com/wiki/Grigori
The fact that he has the unit ID 1, the first unit in the game, is deliberate so that people can't wish for Grigoris, or at least they don't get what they expected.