Well, not really, but they went inside the Reactor 3's building to measure the radiation inside the reactor building and take videos. TEPCO hasn't released the data or the video yet.
(The photo is from Yomiuri: Packbot opening the door to the Reactor 3 building.)
From PC World (4/17/2011):
A pair of remote controlled robots entered a reactor building at the stricken Fukushima Daiichi nuclear power plant on Sunday morning for the first time.
Plant operator Tokyo Electric Power is hoping the iRobot Packbots will be able to provide data on the current condition inside the buildings, parts of which contain high levels of radioactivity and are hazardous for workers to enter.
The robots entered the plant's number 3 reactor building and were due to take radiation and temperature readings. They are equipped with video cameras that can provide a live feed to operators.Photos released by Tokyo Electric Power (TEPCO) showed one of the robots manipulating a handle on the second of a pair of double doors that lead into the reactor building.
TEPCO has yet to release any information about what the robots found inside the building. If the mission proves a success, the robots will also be used inside the adjacent reactor buildings 1 and 2 at the plant.
Yomiuri Shinbun reports that a worker at the plant measured the radiation level from outside the door to the Reactor 3 building on Saturday, and it was 270 milli-sievert/hour.
The data from the iRobots will be used by TEPCO to determine how long the workers would be able to stay inside the reactor buildings for repairs.