Yes, I have successfully gotten this to work in a MODIFIED Bushnell Trophy Cam HD.
Let me explain the modification - since most game camera's are meant to last a long time on a set of batteries they shut off power to the SD card as soon as they're done writing the data to the card - this isn't enough time for the eyefi to power up and transmit the image.
So for anyone else who wants to do this just like Irritantno9 said you have to hack in 3.3v power to the GND and VCC pins. In the Trophy Cam this involves removing a few screws, soldering two wires onto the SD card reader, soldering two wires to the DC power supply terminals on the circuit board, then using a LM317 and two resistors (or similar setup) to step down from 6v to 3.3v for the eyefi card.
So yes it can be done, and with a minimum of fuss if you are comfortable doing some very basic soldering.